I've seen lists of the voice actors before. (Check out
this link for starters.) Most of them have done voices for animated programs, but unfortunately, I haven't seen/heard their work before. The one notable exception is David Warner (Jon Irenicus), who has done a lot of on-screen acting. He has appeared in movies such as
Titanic (the ex-cop who works for the millionaire) and
The Man With Two Brains (a scientist), among others, including the forgettable Star Trek movie that The Fallen One couldn't remember the name of.

(He actually appeared in
two forgettable
Star Trek movies.)
In my opinion, just about all of the voice acting in BG1 and BG2 is great. Occasionally, there are oddities and inconsistencies; for example, if Uncle Lester has a southern American accent, why does his nephew have a working-class English accent? But actually, it's even funnier that way. Ribald's accent seems out-of-place, but since he has so many good lines, it doesn't matter. ("What can we do to make your dreams come true today?" ) My favorite voices would have to be those of Jon Irenicus, Minsc, and the new NPC in Throne of Bhaal. They're not necessarily the most charming, but they are definitely the most memorable to me.
According to a list I just saw at the
Bioware Forums, Renal Bloodscalp's voice was done by Maurice LaMarche, who also did the voices of Yoshimo, Chief Inspector Brega, Minister Lloyd, the Avatar Of Rillifane, and Hendak. Most of the voice actors did the voices of more than one character; since voice acting is what they do for a living, they are talented enough to handle more than one character. Can you believe that the actress who did the voice of Nalia also did the voice of Viconia in BG2? Or that the actor who did the voice of Gorion also did the voice of Minsc?
Here's an edited list of voice actors. (I've added a few of the characters from BG1, using the list found
here.) If you want to see the original lists, which contain more characters, just follow the links above.
Charlie Adler: Kalah, Teos, Rielev, The Thumb, Rejiek Hidesman, Samuel Thunderburp, Greed Demon, Uncle Lester, Shade Lord
Michael Bell: Haer’Dalis, Vittorio the Drunken Lout, Male Merchant ("You'll find no better prices in Amn..."?)
Jeff Bennett: Xan, Drizzt, Saemon Havarian, Pride Demon, Quayle (BG1)
Gregg Berger: Simyaz, Isaea Roenal, Oisig Highwatcher
Cam Clarke: Aran Linvail, Shank
Jonathan Cook: Tor'Gal, Lavok, Sassar
Jim Cummings: Minsc, Gorion, Enslaved Genie, Lord Jierden, Kahn Xahraa (Trademeet), Selfish Demon, Abazigal (TOB), Master Wraith (TOB), Saladrex? (TOB), Mulahey (BG1), Tazok (BG1)
Jennifer Darling: Jaheira (BG1), Shar Teel (BG1)
Grey Delisle: Nalia, Viconia (BG2), Bubbles, Raelis Shai, Skie (BG1)
Melissa Disney: Imoen, Viconia (BG1 only)
Michael Dorn: Bhaal (SoA only)
Bill Farmer: Garren Windspear, Yeslick (BG1)
Brian George: Coran (BG1)
Michael Gough: Solaufein, Gaal, Desharik
Wayne Grace: Elhan, Announcer, Major Domo
Jennifer Hale: Mazzy, Dynaheir (BG1)
Amber Hood: Dili, Alora (BG1), Dryad (BG1), Nymph (BG1)
Rodger L. Jackson: Keldorn
Charity James: Phaere
Nick Jamison: Dradeel, Captain Dennis
Maurice LaMarche: Yoshimo, Renal Bloodscalp, Chief Inspector Brega, Minister Lloyd, Avatar Of Rillifane, Hendak
Tress MacNeille: Edwina, Royal High Priestess Senityilli
John Mariano: Tiax, Talon Yarryl, Naljier, Kagain (BG1)
Jason Marsden: Cernd, Ajantis (BG1)
Bill Martin: Korgan
Jim Meskimen: Edwin, Khalid (BG1)
Alan Oppenheimer: Guardian Telwyn, Sir Sarles, Mornmaster Thaddin Dawnhunter
Jeff Osterhage: Valygar
Valerie Pappas: Valen
Rob Paulsen: Anomen, Biff The Understudy, Kivan (BG1), Prism (BG1), Volo (BG1)
Diane Pershing: Adalon, Safana (BG1), Centeol (BG1), Tamoko (BG1)
David Prince: Ribald, Lieutenant Aegisfield
Kevin Michael Richardson: Sarevok, BG1 Narrator, “You must gather your party before venturing forth”, Yaga-Shura (TOB), Bhaal (ToB)
Neil Ross: Eldoth (BG1), Ogrillon (BG1), Scar (BG1)
Jack Roth: Jan Jansen, Wanev, Carbos
Dwight Schultz: Mae’Var
Hidi Shannon: Jaheira (BG2), Melissan (TOB), Black Lily (BG1), Faldorn (BG1), Silke (BG1)
Jane Singer: Branwen (BG2)
Kath Soucie: Aerie, Aphril, Ellesime, Priss, Young Sarevok (TOB)
Bernadette Sullivan: Branwen (BG1)
John Vernon: Goldander Blackenrock, Baron Ployer
B.J. Ward: Faldorn, Bodhi, Lady Maria, Lady Delcia
David Warner: Jon Irenicus
Frank Welker: Terminsel (SoA only), Avatar of Amaunator, King Ixilthetocal, Kirinaldo, Xzar (BG1), Duke Eltan (BG1), Elminster (BG1), Korax (BG1)
Billy West: Lehtinan, Gaelan