Well, Slipknot and Limp Bizkuit tune down to around A, but they also use seven strings so they're really only tuning down a full step.

Along the detuning line, I suggest you check out Scissorfight. I'm not the least bit a fan of L.B. or Slipknot but this band here rules, and what's more is the guitarist uses a normal six string tuned something like A-E-B-G-B-E (though I'm not entirely sure how he tunes). To get his sound you only need an old Marshall, a Les Paul, and some really ballsy strings. They've got three songs up on their site for people to download though if you've got some kind of downloading program, I suggest you try and find "The Gibbetted Captain Kidd," "The Most Dangerous Animal is Me," and "Helicopter Killing Cotton Mouth."

One word of warning: Guitar amps aren't exactly designed to handle pitches that low, so be careful because speakers can get expensive. Also, you may want to think about keeping one guitar detuned (and have it set up for that), and leave the others in standard tuning (or a half step down like you have it now).