I cleared nearly three gigs of space on my iPhone, and you can too!!! Here's how..

While rippin through my phone using iFile, I noticed a folder that was a cache of pics from texting. That seems about right. However, some of these were pics from threads I had deleted long, long ago. So I took some time, about three hours, to go through the entire folder and determine what I wanted to keep and what I wanted to delete. In the end, I cleared 2.8 Gigs of cached pics. Apparently I text pics back and forth often. Go to folder /Var/Mobile/Library/SMS/. Inside there, you'll find folders labelled Attachments, Drafts and Parts. Attachments has all the cache of pics you've ever sent or received in a text. Once you delete the file out of attachments, you likely wont see too many in the Parts folder. Don't worry about deleting the entire folder either, it's ok to do so. If you send or receive another pic, or any other media file, your phone will simply create another folder in /Var/Mobile/Library/SMS/. Hope this helps!!
Edit: I'm rockin an iPhone 4 on iOS 6.1.2 and Cydia 1.1.8
EDIT 2: I HAVE A THEORY AS WELL. If you restore your phone to an old restore point, say from a couple years ago, jailbroke it again and went into the same folder (/Var/Mobile/Library/SMS/), you might find even older pics. But it's just a theory. I may try it one day and when I do, I'll be sure to give a heads up

EDIT 3: Looks like I just cleared another ton of space without any adverse effects. About another Gig in fact. I found just over 2,000 files at anywhere from 3Kb to 12Kb in the imageCache folder, located in /var/mobile/Library/Caches/imageCache. I looked at around 50 of these files and they all seem to be images cached from the appstore, itunes, etc..
Deleted em all, emptied the trash, no adverse effects, more space!!