Leonardo DiCaprio is kind of amazing to me... he's still fairly young but the big names who he runs with are unreal. He's not going anywhere, and I love his films. He's got a lot of range too, few in Hollywood have gone from severely handicapped (What's Eating Gilbert Grape), to a horribly torn undercover cop with serious issues of his own (The Departed), and complex roles that require copious amounts of study almost to the point of driving himself mad (The Aviator). It's rare you see his maturity in Hollywood too. After Titanic, he kind of disappeared for a while because he didnt want to be type cast, and didnt want to be the biggest thing in the world, and then go simmering out like a roman candle.
I love Tom Hanks, Eric Bana and some other big names in Hollywood. I like a bunch of non-A list actors too though, indi films are a lot of fun to try and discover. Blockbusters dont always do it for me. Henry Fonda's films are always good times.
In terms of female actors, Judi Dench is a fox

Scarlette is great, and there are some other lesse knowns like Imogen Poots.