Here's an interesting list Alternate Guitar Tunings from a number of bands and musicians ranging from joni mitchell to metallica. There are short clips of the songs so you get to hear what the alternate tuning sound like.
Very cool breakdown of famous work using this method. The part I've always liked is that truly, there isn't any rule set-there are tunings that came before, but tweaking the instrument in your own way is a pretty cool thing to try...especially when there's fuzz involved. Slight detunes and dissonance...mmmm...
Also-the more strings, the more possibilities...though it's easy as hell to get lost on an acoustic twelve string.
I used some kind of "by ear" alternate tuning not too long ago on electric bass when I made some loops for a friend to use. I also played with a glass guitar slide...that was tough as the strings on the bass are waaaay fatter and harder to fret than on the guitar!
The fun doesn't start until you mess with the tuning... I used a cool one on First Day Apart. I stuck to standard for Radha's Tears, but that has me stretching a lot. Probably won't use standard again. Right now I'm messing with a half-high-strung tuning (the middle two strings are an octave higher) that yielded me a pretty cool acoustic tune. On the electric it should be even better. And I've barely started with my custom fretless guitar and EBow...