Inspired by Rick's Faggggedaboudit! thread, Here is something I'm very excited about having learned. It is particular to guitar (perhaps otherwise applicable or adaptable?) and my teacher calls it the Caged method.

You can play a chord, say for example a G. Then you can play a G chord in a C fingering but in another place on the neck. You can also play a G chord using the A, E, and D fingerings but respectivly in different places on the neck.

It opens up a world of possibilities when you're figuring out variations or just figuring out melodies. My apologies if this has already been covered. I hate beating a dead horse... :o) Margo