Mel Blanc, of course!! He's like the king of voice actors. May he rest in peace. Oh, and yes, he did voice Elmer Fudd. You can hear it through other characters slightly.
Rob Paulsen is a talented voice actor as well. I love his voice, and he seem to always voice fav characters for me. lol
June Forray, she was like the queen of voice actors back in her day. She voiced a grand amt of female characters, just as Mel Blanc voiced lots of male characters.
Mona Marshall, she's a very talented VA imo. She's done a tone of voice work, from Koushirou "Izzy" Izumi in Digimon Adventure/Adventure 02 (US version), to Wendy in South Park, to some voice work on Rainbow Brite (iirc), and seems no matter what, the voice is always different.
Just about everyone already mentioned is a favorite of mine. My personal favorites are Mark Hamill, Steven Blum, Robert Whicks, and Wendee Lee. I just recently got Steve Blum's autograph so that pushes him up a bit further than he already was.
People don't just dismiss Billy West in one or two posts. He is the best going around for geting inside a character and pushing emotion and humor through. His work on Futurama is enough to justify him being on here