GTA IV.

Vlad was a hoot.

Gabriel Knight, definitely, courtesy of Tim Cury and Mark Hammil!

Ok, now I'm disappointed. No one mentionned Sacrifice (at least Tim Curry is mentionned).

Edit : my bad, Licurg did his job.

L.A. Noire.
Definitely the best voice acting in a game, it was really great. (most of the cast from madmen)
Other than that i'd say Mass Effect.

Andy Milder as Sebastian Lacroix in Vampire: The Masquerade - Bloodlines.

Mass Effect series, except for some cringe inducing lines by Jennifer Hale. Don't get me wrong... she's great when she does it right but there are some parts that are overacted.

Well pointed out!

Hector: Badge of Carnage features good VA, and is all the more remarkable since one actor voiced all of the male characters.

Total Annihilation campaign narration by James Earl Jones,, it doesn't get any better than that!

I think it's hard to say; it's reached the point where high-quality acting in big-budget games seems to be the rule rather than the exception. I'd give a shout-out to the Bastian narrator (Logan Cunningham), and the various Portal and Planescape actors, but not prepared to single any one performance out as "best."

Brütal Legend. All of it. Every bit. So much awesome. Jack Black, Rob Halford, and Tim Curry especially though.
The Bard's Tale is fantastically well done.
Whomever does Baeloth the Entertainer in BGEE is perfect for the character.
The Witcher has some solid voice acting and I remember being impressed with the voice acting in Stronghold HD. And of course the narrator in Dungeon Keeper.

Gabriel Knight 1
The Last Express
Gemini Rue
The Longest Journey / Dreamfall

Shin Megami Tensei: Persona 4 has my favourite. Which is peculiar, because it's an English dub of a Japanese game.

EDIT: I've only really played 2 hours of it (trying to beat P3 first) but I haven't cringed a single time yet. It just flows so beautifully.

Original: I guess Grim Fandango deserves some love...
Dubbing: I really, really loved what CD Project did with Planescape: Torment for polish market.

It's...a really hard question.

There are SO many games with good voice acting. If I had to limit myself to those I bought on GOG, these would include:

- All those made by Bioware (including MDK2)
- Beyond Good and Evil
- Alan Wake
- Broken Sword (all of them)
- King's Quest VI
- Gabriel Knight
- Jagged Alliance (First one. Haven't played the second one)

There may be others that I should have considered (I considered The Longest Journey, but I haven't played it long enough to judge the voice acting of all the characters).

Yes, I've just started the series with MGS1 - David Hayter sounds perfect as Snake, and I had to look up the voice for Naomi and surprised to learn it was more greatness from Jennifer Hale. Undoubtedly one of the best female voices ever.

I also really enjoyed Claudia Black in Uncharted 2 (although graphically, her eyes never looked right and it always freaked me out). Nolan North, of course, and Graham McTavish as the big bad.

Likewise on PS3, Heavenly Sword starring the sultry vocals of Anna Torv and Andy Serkis - made these characters feel completely real to me. Not just motion captured, they really captured the emotion.

I remember being enchanted with Sarah Hamilton as April Ryan in The Longest Journey - I could listen to her talking about that rubber ducky all day. :D

Lots of others mentioned in this thread, too. Stephen Russell as Garrett in the Thief series is perfection. As is Chris Jones as Tex Murphy.

I'll also give a shout to Michael Ironside in the Tom Clancy Splinter Cell games. And in the second game, Dennis Haysbert as the team leader, is like playing an episode of 24 or The Unit.