Jeff Bennett - Currently what surprises me is his roles in Stroker & Hoop and the Boondocks where (like Tara ala Drawn Together) I heard him curse for the first time a few years back. Not only that, in the Boondocks, he got away with saying the N-Word. Although when I was little, this guy use to wow from voice to voice, for a while I couldn't pin him down. Brooklyn, Bravo, Lord Bravery, Huntsman, Cave Guy, Dexter's Dad this guy is awesome.
Dee Baker - This guy did Olmec, Numbah 4, Cow & Chicken's Dad and Viewtiful Joe? (in the games only), very impressive.
Rob Paulsen - Mostly I can hear him in his voices, but every so often he'll stun ya with Yakko, Pinky, Tudrussell or Throttle (Biker Mice), the latter two are very impressive.
Scott McNeil - So good, I didn't know he was Bonesteel.
Matt Hill - Like Paulsen, I can spot his voice usually, but Ed from EEnE came out of now...where.
Gray Delise - The female Jeff Bennett, once you hear all her voices you can spot her, but she has a ton. You wouldn't be able to tell me that Azula, Mandy, Vicky, Major Doctor Ghastly, Lor from the Weekenders and the current Daphne of Scooby Doo voice and her Scottish cousin were the same person right off the bat.
Tom Kenny - Mainly for his Heffer voice, one of a kind.
Mr. Lawrence - How he goes from Filbert, Edward from Camp Lazlo and Plankton is pretty awesome, and he's an animator too.
Steve Blum - When he isn't doing every anime in hollywood, he takes time to do a remarkable Green Goblin and Jamie (MegasXLR) a laid back slacker of which he pulls off surprisingly well.
Cree Summer - Cree Lincoln is and will always be one of her best voices.
John C. McGinley - Dr. Cox as the Atom and the White Shadow? I'm still in shock.
Jaleel White - Replace Dr. Cox with Urkel and Atom and White Shadow Sonic the Hedgehog.
I keep expecting Sausuke Uchiha's voice when I see Yuri Lowenthal's name in the credits, instead he makes me wonder, does he really voice Sho Yamato (Idaten Jump), Superman of LoSH, and a 15 year old Ben 10?
Corey Burton - Over the years, this guy keeps coming up with new voices and except for his Captain Hook voice (notably from Kingdom Hearts) he really doesn't seem to reuse many of his voices he has too much. From Dale (Rescue Rangers KHII) to Megatron (TF:Animated) to Brainiac (Superman, JLU) this guy always shocks me as I always think it's someone new. IMHO, Corey Burton is a legend.