People come here asking what light they should get rather often, and a few models get recommended often. I've made an arbitrary list of popular lights you should consider if you're shopping for a light.

Briefly, here are some characteristics that are usually considered desirable. Most of the recommended lights won't have all of them, but these are things to look for when shopping for lights:

• Neutral white tint - the vast majority of people with an opinion prefer a color temperature that's within the range of direct sunlight, which is generally marketed as "neutral white", but sometimes as "warm white"
• A lack of red, or especially green off-tints, beam artifacts and tint shift from the center of the beam to the edges
• A user interface that does not require cycling through different modes to turn off, and does not change modes every time the light is turned off
• A lack of blinking modes within the standard mode rotation, either because the light doesn't have any, or they're "hidden" by being accessed in a different manner than the usual modes
• An IP waterproofing rating - most good lights are rated for IPX8 with the depth and duration of submersion specified by the manufacturer
• A lack of timed stepdowns. Some lights only produce their maximum output for a few minutes at a time. While some powerful lights can get too hot to hold if run on high constantly, the hardware necessary to measure temperature and only reduce power if the light is actually too hot costs only a few cents, but many lights won't overheat badly anyway
• Full-spectrum, or high-CRI for more accurate color rendering. Color rendering index, or CRI is the most common measurement of this; average LEDs are about 65. Over 80 is decent, and over 90 is excellent. The highest I've heard of from an LED is 97.
• A sub-lumen moonlight mode (for general-use lights)
• A user interface that allows access to the lowest and highest modes from off without having to cycle through other modes

About specs

Lumens are total output. Don't worry about small differences in output. You probably can't detect a 10% difference in lumens with your eyes. It takes 4 times the lumens to look twice as bright. Candela is intensity, which translates to throw distance. FL1 throw numbers are about right for detecting large objects; cut them in half for seeing clearly. FL1 runtime numbers are to 10% output and can be misleading. Look for a review with a runtime graph.

If you want something particularly powerful or long-lasting, you should probably skip right to the 18650-powered lights. This battery significantly outperforms other options, especially alkalines.

So, on to the list, by general category:

Keychain lights

(Other than 1xAAA)

• Nitecore Tube - a brighter, variable output, USB-charging replacement for button-cell keychain lights with shortcuts to high and low modes from off. $10
• Nitecore TIP CRI - a bigger Tube with more output, neutral white tint, 90+ CRI and a dual-switch user interface that has shortcuts to low, high and last-used modes. $35
• The Cooyoo Quantum, and rebranded versions by several manufacturers such as the Fenix UC02. There are versions in more exotic metals including stainless steel, copper and titanium. This uses a removable 10180 size Li-ion battery and has USB charging. $25 (for the Fenix in aluminum)

1xAAA lights

• Thrunite Ti3 - 3-mode with a twisty switch, available in neutral white. Starts in a sub-lumen moonlight mode if it has been off for longer than 10 seconds. $20
• Thrunite Ti - the Ti3 in titanium. Currently the same price, and shiny, so why not? $20
• Thrunite Ti5 - a Ti3 with a tailswitch. Available in aluminum and titanium. $17
• Peak Eiger - a high-end option. Made in the US by a small shop, fully adjustable brightness using quantum tunneling composite. High-CRI available and recommended. $50

2xAAA lights

• Thrunite Ti4 - this is a longer, brighter Ti5. Neutral white available. Titanium available. $20
• Lumintop IYP365 Nichia 219B - 90+ CRI (Nichia version only) and neutral white. Not as bright as a Ti4, but light quality is often more important for being able to see clearly. $24

1xAA lights

• Zebralight SC52w - neutral white, e-switch with shortcuts to low, medium and high with several sub-levels for each. $59
• Thrunite T10 - available neutral white, similar to a larger Ti5. Available in aluminum or titanium. $22
• Olight S1A - optional neutral white, e-switch. $50

1xCR123/16340 lights

• Olight S1 - very small, cool white in the aluminum version. There are neutral white versions in other, more expensive metals. $50
• Eagletac D25C Clicky Nichia - very small given the tailswitch, high-CRI neutral white with the optional Nichia 219B. $50

18650 straight-body dual-switch lights

This category is so popular, there's a comparison chart in the sidebar. These are the ones I like.

• Thrunite TN12 - comes in neutral white, has a separate mode switch, can tailstand, has a moonlight mode, modes appear evenly-spaced. This may well be the most frequently recommended light on r/flashlight. $50
• Acebeam EC35 Bestlight.io edition - neutral white and long throw for this size class, with several body color options. Otherwise similar to a TN12. This variant became available after u/mcfarlie6996 reviewed a shorter-throwing cool white EC35 and said it should be offered with a different LED. Only available from Bestlight.io. $65
• Eagletac DX30LC2 - slimmer than most 18650 lights, with a unique take on the dual-switch interface: it always starts on high, unless the mode switch is held, in which case it starts on low. Longer throw than most, neutral white available from some dealers. $75
• Armytek Partner C2 Pro XHP35 - the highest output in this class, thermal sensor to prevent overheating, boost driver, warm-neutral white available. $95
• Atactical A1 - reportedly manufactured by Thrunite for Atactical. This light doesn't have most of the qualities we like to see, but it seems to be reliable and comes with a battery that has a USB charging port on it. $20
• Thrunite TC12 - essentially a TN12 with USB charging, a thermal sensor to limit temperature, low-voltage protection and a battery included. $70

18650 right-angle lights

These can be used as headlamps or handhelds. Most come with a headband and a pocket clip. We *should have a comparison chart.

• Skilhunt H03 - this version has a honeycomb TIR optic for a diffuse beam pattern. A reflector for more throw and a version with a reflector and a flip-out diffuser exist. Uses a timed stepdown. Available in neutral white. $30 (from certain dealers with a coupon code; there always seems to be a code available)
• Armytek Wizard - essentially a Skillhunt H03 with a higher impact-resistance rating and a thermal sensor instead of a timed stepdown. $45
• Armytek Wizard Magnet USB - the above with a magnetic connector to charge the battery inside the light and a battery included. $65
• Armytek Wizard Pro - the Wizard, with more output, a couple extra modes and a boost driver for stable output. $81
• Armytek Wizard Pro Magnet USB - do I really have to explain what this is? $85
• Zebralight H600w - very compact, neutral white, well-regarded user interface, boost driver. What's not to love? Oh, yeah, pocket clip not included (you can buy an Armytek Wizard clip to use with it) $89
• Zebralight H600Fd - the above with 80+ CRI, a frosted lens for a more diffuse beam and a slightly cooler neutral tint that's a close match for the midday sun. $89
• Zebralight H600Fc - the H600Fd, but with warmer tint, like the late afternoon sun. $89
• Zebralight H603d - the H600Fd with no reflector and a clear lens for a very floody, perfectly even beam. $89
• Zebralight H603c - if you've read the above, this needs no explanation. $89

Other pocketable 18650 lights

These have various switch types and fit reasonably well in a pocket

• Zebralight SC63w - side switch, very compact, neutral white, well-regarded user interface, boost driver. This is a favorite for EDC. $79
• Armytek Prime C2 Pro XP-L - high impact resistance, warm-neutral white, shortcuts to low and last-used from off. $60
• Armytek Prime C2 Pro XHP35 - the above with higher brightness and a boost driver for stable output. $90
• Armytek Partner C2 - tailswitch with momentary, locks on high with the head tightened. The mode locking makes this light good for high-stress situations and handing to other people during an emergency. Warm-neutral tint. $55
• Convoy S-series - Popular light for DIY and modification. Many parts are available from the manufacturer and Mountain Electronics. S2+ linked. S3 is similar, but with a removable steel bezel. S6 has a deeper reflector for a narrower spill and longer throw. The new Biscotti firmware is available for an extra dollar. Several build-to-order options are available. More 7135 chips = more brightness and heat, less battery life. Several tints available - higher numbers are warmer (1A is very cool, 7A is very warm, 4C is fairly neutral). Clicky tailswitch, without momentary. $20-ish
• BLF A6, AKA Astrolux S1 - the original BLF/Banggood collaboration to produce something similar to how a DIYer might hot-rod a Convoy S2+. Nicer user interface than old-firmware Convoys. As above, higher numbers are warmer for the tint. 3D is neutral. $20-30

Duty lights

These are suitable for first responders and possibly members of the military in combat roles. The focus is on simple operation, reliability and a good way to make sure the light starts on high. The Armytek lights here are well-suited to mounting on long guns.

• Armytek Dobermann Pro XHP35 - tailswitch with half-press for momentary, locks on high when the head is tightened, blinks through modes when the head is loose. Narrow spill with moderately long throw. Boost driver for stable output. Warm-neutral tint cuts through fog better than cool white and reduces glare. $90
• Armytek Viking Pro XHP50 - the above with a larger head, larger LED and a wider beam for more flood and less throw. $100
• Armytek Predator Pro XHP35 - like the Viking, but with a smaller LED for a more focused hotspot and longer throw than the Viking or Dobermann. $100
• Klarus XT11GT - two tail switches and one side switch with three user interface configurations make for more of a learning curve with this light, gives the user the ability to get it to come on in the mode they want when they want it. USB charging. Battery included. Cool white only. $90
• Eagletac GX30L2-DR - for those who want a better Streamlight Stinger. 2x18650. Front emitter for throw. Side emitters with built-in diffuser to flood an area or use as a traffic wand. Onboard charging. Neutral white optional. The included battery pack is just two 18650s in series. It says not to charge standard 18650s, but there's no technical reason for that, and it is reported to work. Protected cells recommended. $145

High-performance lights

Huge output, long throw, etc....

• Thrunite TN40S - high output with long throw in the style of the Nitecore TM16GT, but... more. 4x18650. Neutral white available and strongly recommended if you want to see anything but the haze you didn't know was there. $200
• Thrunite TN42 - 1550m FL1 throw advertised. You're probably thinking "that can't be right, has anybody tested this?". Reviewers have, and you're right: 1550m is inaccurate. It's more like 1700. Neutral white even more strongly recommended. 4x18650. $200
• Noctigon Meteor M43 - with a mere 7000 lumens, it's not as bright as an Olight X7, but I think this is still the best soup can light going. Nichia 219C version recommended for a combination of high output and 80+ CRI. 219B to maximize CRI at the expense of output. Other emitters not recommended. 4x18650. $128
• Convoy L6 - the budget high-output light. 3800 lumens and about 500m FL1 throw compare well with a lot of $200 lights. 3A tint is the most neutral and therefore recommended, but some do like the warmer 5C. 2x26650. 2x18650 is possible with a sleeve. $50

This is far from a comprehensive list, so if I left your favorite light out it's obviously because I think it's crap and hate you for liking it, not because this post is already 16K chars long and I'm tired of typing.