Isn't Robert Randolph a Steel Guitar player? Big difference from that and slide. He is great, though.
Warren Haynes, Duane Allman, Derek Trucks, Robin trower (of course, Clapton, SRV etc, etc, etc), Henry Garza (Los Lonely Boys).
The 1st three are excellent slide players (Derek has that vocal sound down pat, and somehow gets a tone that's like half-melted butter. It's awesome--get a copy of "Joyful Noise", that's the album, and the title track). Warren is just the man of the hour (plays in 3 bands right now).
I don't listen to him much anymore, but Zakk Wylde will always be great, I just kinda' got convicted of his sometimes vulgar lyrics (the music is slammin' though). I'm going to try to get this man saved. Especially since his buddy Dimebag Darrell just died (the shooting last week in Columbus), I figured it's a good time to write him a letter--I am for real about this one. There are not ANY Christian guitar heroes. That's very upsetting to me.
I better stop before I get on my soap box. Sorry.