I am surprised that no one has mentioned Lawrence Fishburne yet. He commands the screen in any movie he is in, whether as Morpheus or as Furious Styles. Don Cheadle is a very good choice. Phillip Seymour Hoffman is quite good, as is Ian McKellan, Kevin Spacey, Kate Winslett, Gary Oldman, David Thewlis, Robert DuVall, Meryl Streep and Hellen Mirren and Judy Dench- the skill that each of these actors has to so totally immerse themselves in their character that you forget that they are stars. As opposed to, say, Tom Cruise, who no matter what movie he is in you cannot forget you are watching Tom Cruise. Even though she is getting overexposed I also think Scarlett Johanssen is a good actor. I might also include Johnny Depp here since he rarely, outside of Pirates, picks easy movies.
I do not find Tom Cruise, Brad Pitt, Angelina Jolie, Jennifer Aniston or any of that ilk particularly watchable, and think they are overrated as actors, though I might consider Pitt a step above the others.