Dragons especially the Blue
Goblinoids (all of them- goblins, hobgoblins, bugbears, norkers, koalinth, etc.)
Devils especially Pit Fiends and Eyrines
Minotaurs
Minotaurs, nagas, and especially yuan-ti. The latter are perfect for the Lovecraftian devolved race of lore that lurks in the deep wilderness and harbours terrible secrets or the Howardesque superintelligent snake people who are survivors of an elder age and treat humans like playthings. I especially liked the Nyambe take on them, where they were trying to awaken the last survivors of their their progenitor species.
Has to be Illithids..love the Cthuloid vibe, and for sheer monster rampage fun- Mr Owlbear. Ever since I saw my first one 12 years ago I've liked 'em. They represent the wierdness and fantasy of D&D- and they kick PC ass but good.