Gary Oldman would be my choice for best actor around.
Robin Williams and Jim Carrey are two comedians that don't always get the credit they deserve, but very few actors would be able to do what they do. I'd like to see some of the best actor recipients do what Carrey did in 'The Mask' or Williams in 'Good Morning Vietnam'.
Actors I generally like are Daniel Day-Lewis, Ian McShane, Liam Neeson, Bruce Willis, Ed Harris, Brad Dourif, Viggo Mortensen, Tom Hanks, Christopher Lee, Peter Dinklage, Sean Bean and Ian Mckellen. Just because they are true actors that do the job and aren't huge celebrity types.
Also don't mind Sean Penn, Al Pacino, Matt Damon and any other actors that get into the directing, producing, writing or general movie making part of production instead of being on set for a few weeks and saying a few lines like a lot of actors do. I generally don't like the acting 'profession' as I think they get WAY too much credit for the movies they are in, while directors, writers etc are pushed to the background, even though most of the time their job is much harder. Then it gets to the part where some celebrities are paid $20 million just to be in a movie. Some actors considered the greatest ever, like Marlon Brando, often didn't listen to the director, didn't learn their lines and were barely on set while demanding ridiculous salaries. For the talent and work required, I don't think most actors deserve the credit, money or the celebrity standing and influence they have. Some films, like Tropic Thunder and Team America, mock this situation brilliantly.
Also when it comes to voice actors I have great respect for Mel Blanc, Billy West, Mark Hamill and Dan Castallaneta, great talent without the recognition screen actors get.