For those just starting into this kind of electronica, here is sort of a guide. I'll just stick to probably the three most well known artists; Aphex Twin, Boards of Canada, and Autechre. Although definitely also go for Squarepusher, and the many earlier guises of Aphex Twin (Afx, polygon window, caustic window, ect.) and Gescom (if you can find it)
Boards of Canada: I guess I'm in the minority here, but this is the boc album i started with and I think it's the best. But then, I'm the type to buy every release by a group if i like them enough. Needless to say, I have every boc release and am eagerly awaiting the repressing of Twoism.
Autechre: I am a firm beliver in diving headfirst into an artist's most challenging work. The first Autechre album I bought was Confield, but I'm going to reccomend both EP7 and LP5, unfortuneatly two of the most difficult albums to get a hold of in the US (although if you live in portland, everyday music is a pretty good place to look.) One word: AMAZON. This is group that is so diverse, not one of their records is redundant. EP7 and LP% are drastically different both from each other and from the rest of the Autechre catalog. Every single song on each is a classic. Just get the mwhile you still can.
Aphex Twin: I Care Because You Do. Hands down one of the best electronica records out there. This guy is the father of this type of music, and the record is the epitome of his career. Has the bonus of being very easy to find in the US.
You'll notice that i didnt really describe the sound of any of these records. One reason is that it's pretty hard to do that, but I figure if you're reading this thread, you want to try new types of music, or have maybe heard one or two songs from these guys.