I love experimenting with different guitar tunings. It's fun to take everything you know about how to make chords in standard tuning (eadgbe) and throw it out the window. I began experimenting with different guitar tunings very soon after I started to learn how to play. One of the first I fooled around with was one I made up, although I'm sure it's been used before, I just have never seen it used anywhere else. It's (dadabe) The problem is tuning the g up to an a, careful, I've had the string snap many times when tuning up. The reason I ended up with this tuning is I couldn't reach a particular chord I was trying to hit unless I tuned the G up an A, and I was already in drop D.
One tuning that I've really enjoyed screwing around with lately is based on the G "mali" tuning. E up to G, A down to G, D,G, B and E stay the same. Pretty simple!(ggdgbe) This is basically a g-major 6 tuning and you can use both g's as a powerful drone while you go nuts on the strings above. Tweak the b down to a b-flat and now you have a g-minor with a mean sounding tri-tone on top(ggdg b-flat e) Now, for yet another cool sound, tweak the e up a half step to an f. Now you have (ggdg b-flat f) which is a g minor 7th chord.
I love experimenting with different tunings on a banjo as well, but I'm not going to go into that right now, just tune the b up to c for a sus4 sound known as the "high and lonesome sound." This was a common tuning used by pickers in the appalachian mountains around the turn of the century. (gdgcd)