My favorite trick is the one Mike mentioned in the start of this thread "playing a G, C, and D chord on the guitar while keeping the notes D and G on the top two strings (making a G, Cadd9, and D sus4)." That's how I always play in G, plus you can play an Em with the D and G still anchored on the high strings (which makes it an Em7, I believe. This is a trick I first learned from the Smashing Pumpkins' "Disarm."

I also like to slide a first position D chord up and down the neck while keeping the open D string as a drone. In different positions this gives you cool slash chords like E/D, G/D. A/D etc. A first position A chord also sounds great played up and down the neck with the open A string ringing.

You can also do cool things with a Drop D, or even a Double Drop D tuning. Try dropping both E strings to D, then slide a first position E chord up and down the neck while letting both "D" strings ring. It's gnarly.

Chris Jay Becker
Hallelujah Street Music