No particular order my top 3,
Steven J. Blum http://www.imdb.com/name/nm0089710/ - seriously, look at his career, and you ALWAYS know when it's Blum doing a voice.
Jennifer Hale http://www.imdb.com/name/nm0354937/ - God, i love her voice, you can always tell a Hale character, with ehr perfect diction and emotion being rolled into the character.
David Hayter http://www.imdb.com/name/nm0371684/ - We all know him as Solid Snake, but he's had a long and successful career, especially on the writing front (did the screenplays for X-Men, X2 and Watchmen notably - all awesome films)
(Talking proper voice actors here, not actors doing a one off dip into the gaming industry, otherwise there'd be more names.)