The most consistently brilliant film actor has got to be Robert De Niro. Al Pacino comes a close second. They've both been in films that were badly written and/or directed. But those movies are still worth watching simply because those guys are so good at what they do.
Way too many to list, though I do like Dustin Hoffman, Al Pacino, Robert De Niro, Tom Cruise, Gene Hackman, Sean Connery, Denzel Washington... to name a few.