BioShock. Every time Cohen, Ryan, Fontaine or Atlas started talking I stopped all movement to hear every word. Also, bonus points for the characters almost never being physically there and still selling their lines.
Baldur's Gate II. I rolled another character the other day and decided to look up the voice actors. Anomen's is Robert Paulson, who's only been in EVERY cartoon I watched as a kid (f.e. Pinky from Pinky & the Brain, David Warner voiced Irenicus, Jason Marsden voiced Cernd... all actors I adore.
Basically though, Bioware games always have great voice acting. I found the Dragon Age (Origins, Awakening and II) cast to be a treat, as well as ME2's.
I'm probably one of the only people who hated Half-Life 2's voice acting. The NPCs had about five voices between them, and their continuous "OMG IT'S FREEMAN" got on my nerves. The important NPCs never managed to sound real to me; it was all fake, play-acting.