Best voice-over work in a video game, All-Time.

[Au Naturel.]

The Prince in PoP : Sands of Time, and Grimoire Weiss in NieR.

They really stick out for me.

 

[aarontg]

Tychus from starcraft 2. Hell.......it's about time.

 

[RemytheNinja]

Kieth David is awesome. When he speaks you know its him.
Other mentions are Claudia Black and Jennifer Hale.