This photo from indigitec.com is a chart of a bunch of useful scales. It demonstrates my need for mastery. I've been playing guitar for almost 8 years now, but it's a hobby that requires constant practice and dedication. The photo reminds me to practice and also provides some useful information.
A chord progression cheat sheet I made after discovering the greatness of the chord-numbering system. Once you know all the chords in any major scale you can use this number system to jam or write songs.