I use a glass slide; it sounds "warmer" to me than metal (chrome, copper etc). I play some slide, but use standard tuning mostly (only have 1 electric and there's no time to retune when rehearsing or gigging). Open tunings I've tried are E and G. They squash the box pattern notes closer together so the slide doesn't need to travel as far to cover the scales.

Here's some more sites to check out.


http://www2.one.net.au/~gighire/slide.html

http://www.slideguitar.com/index.html

http://www.slideguitar.com/guitstuff/slinks.htm