Cliff Martinez just did a terrific job with Drive. Ennio Morricone, of course. Ipecac Records (the label run by Mike Patton from Faith No More) put out a great compilation of his more obscure work called Crime and Dissonance. Highly recommended. The soundtrack to Vampyros Lesbos is pretty great too. It's done by a couple German cats whose name I can't remember. It's on a label called Crippled Dick Hot Wax! who have put out a lot of great soundtracks to obscure trash films. I've also always enjoyed Carter Burwell, Fargo in particular. Being a general John Carpenter fanatic has made me a huge fan of his work. Philip Glass and the Kronos Quartet released a score for Tod Browning's Dracula a few years back that is tremendous. Johnny Greenwood knocked it out of the park with There Will Be Blood (but then everyone involved with There Will Be Blood knocked it out of the park) As for my favorites? Cliche, but I have to say Goblin's work on Deep Red, Suspiria and Dawn of the Dead will always be my go to soundtracks.
I have a least favorite as well: James Horner. whenever I see his name on the credits I'm filled with dread. His scores are always overbearing and obnoxious.