The following actors were confirmed to be providing voices:
* Christopher Plummer (The Girl With The Dragon Tattoo, The Insider)
* Max Von Sydow (The Exorcist, Minority Report)
* Joan Allen (The Contender, The Bourne Ultimatum)
* Lynda Carter (Wonder Woman)
* Michael Hogan (Battlestar Galactica)
* Vladimir Kulich (The 13th Warrior, Smoking Aces)
* Claudia Christian (Babylon 5)
* Diane Louise Salinger (Carnivale)
* Renee Victor (Weeds)
* George Coe (Transformers: Dark of the Moon)
Here is a list of voice actors in Skyrim,
now don't be fooled! These guys are probably just voicing main story quest related characters, the filler characters are probably voiced by a much shorter list.
Fallout 3 had its share of celebrity voice actors but everyone still ended up sounding the same.
You always should have a clear leveled perspective of a game you haven't played yet. Think of a long straight line, that is how you should feel until you play the game.
If your line moves up too high before playing the same you may be up for disappointment, if your line moves too low you may not even get the game and your view of the game is permanently impaired.
Right now everyone's lines have skyrocketed in this thread when they should really still have a leveled perspective.