There is just excellent Voice acting throughout SW:TOR. I hate to slight any of the actors by not mentioning them, but I did have a few favorites.
Imperial NPC's :
Grand Moff Regus, as voiced by Julian Sands. That British cat just has the coolest inflections to go along with the Britsh accent. It's a shame his character didn't have a bigger role.
The same can be said for Overseer Tremel, as voiced by Paul Darrow. Really fantastic job.
Player Character's :
The Male Trooper, as voiced by Brian Bloom. I hadn't even realized he was doing professional voice acting, but he knocked it out of the park with the Male Trooper character.