Try some Autechre. Incunabula and Tri Repetae are phenomenal albums by them. Also, check out Mogwai. Not IDM, but still very good.
Thansk for the recs. I've got some Aphex already. I've tried Tricky. There's the occasional song that fits into my listening, but on the whole, a bit too hip hopish for my chill listening pleasure. I'll check out those other bands. It's hard to get a CD that has enough songs, that sustains a certain tone/mood, to buy the whole disc. It's what I like about iTunes the most, just buying a song here or there.