Slayer
Utterly terrible band. The only good aspect of Reign in Blood (supposedly their 'classic' album) is that it's only about half an hour long which makes it almost possible to sit through the entire thing without wanting to pierce my eardrums with an icepick. I never understood how a band this poor became an inspiration for so many bands (unless it was the "ha ha these guys can't play, we can do better" kind of inspiration in which case I totally understand).
Dream Theater
Boring, pretentious, lifeless, emotionless, cheesy. That about sums them up. Don't get why anyone would voluntarily listen to this. Sure they can play their instruments, but what's the point if you can't write a decent song?
Meshuggah
The whole math thing is a nice gimmick but it doesn't seem to make for very interesting music because everything I've heard by them sounds pretty much the same all the way through, boring. And since I'm not a musician and can't really grasp what they are actually doing, the whole technical side of it (if there is any) isn't something I get a kick out of either.
And just large amounts of "true" black metal bands and "brutal/technical" death metal bands in general.
Oh! And anything that somehow involves Mike Patton.