Japanese:
Norio Wakamoto. <url=http://www.youtube.com/watch?v=9V1AEvN8VZs>The man has an awesome voice, whether he's doing villains (Nobunaga, that emperor from Code Geass, Golba from Samurai Shodown) or other roles (Onsokumaru, the narrator from Hayate the Combat Butler, etc.).
Jouji Nakata. The man who voices <url=http://www.youtube.com/watch?v=4J4Fu52Pt14>Sol Badguy, <url=http://www.youtube.com/watch?v=4F6OBtGfVvg&feature=related>Nrvnqsr Chaos, and especially <url=http://www.youtube.com/watch?v=ygA97GqFNPo>Kirei Kotomine (and Alucard, for those who watched Hellsing subbed) has a very sexy deep voice.
English:
Toss-up between James Earl Jones and Christopher Lee. I honestly can't decide...though I lean towards the former.