Tip: Jam Origin Midi Guitar can show every note you play on an interactive circle of fifths.

I just installed the demo, and yes its midi tracking is cool, but I discovered that you can see a live display of all the notes you're playing on a circle of fifths, like this A major chord. You don't even have to purchase the full version (USD$99) to use the feature indefinitely, though you might have to suffer the sound of a direct monitored guitar signal. (If you want a driven amp sound, try adding the SGA1566 plugin to the output.)

It's just really nifty and I wanted to show you guys. It'll show you if you're playing something outside your key, great help if you're composing and want to see what will sound okay. If you want a primer on the circle of fifths or a more complicated one that will do more modes than minor and major, have a look at Interactive Circle of Fifths and its very good user guide.

Happy composing!