the album that really got me interested in the experimental genre, although theres not much like it(that i know of):

edIT - crying over pros for no reason

but yea adding to what kai said, idm is probably the most expansive and diverse genre of edm there is. its got some of the worst music i've ever heard, and the best. i dig that :)

ur gonna have todo some hunting around to find out what u like and what u dont like. couple good places to start would be www.idmtrade.com, and slacker.com experimental section

idm is a very broad term.  it encompasses anything "experimental" pretty much.  so you say squarepusher is experimental drum and bass...well, experimental drum and bass is part of idm. ^.^ i've often heard squarepusher referred to as "drill&bass" or "raggacore." 

that's one thing you'll eventually learn.  there's really no such thing as "idm."  it's just a very vague phrase to encompass anything outside (or leftfield) of the norm in electronic music.