I think Ethan Hawke is a great actor. Gattaca, Before Sunrise, Training Day, Hamlet (modern version).
I'm actually becoming a big fan of Natalie Portman. I really liked both performances in Brothers and V for Vendetta, and now she's set to become one of the biggest actresses in Hollywood when she plays in Darren Aronofsky's Black Swan and Alfonso Cuaron's Gravity. I've heard the performance in Black Swan has made her the front runner for Best Actress at the Oscars.
Edward Norton, Christian Bale, Denzel, De Niro, Pacino, Nicolas Cage, Brad Pitt, Kevin Spacey come to my mind.
Natalie Portman and Ed Norton. Meryl Streep's really good in almost everything I see her in. I like Daniel Craig as Bond. For more "role players", Vince Vaughn, Sam Jackson.
There is so many... But some that I can think of right now... Seth Rogen, James Franco, Jim Carrey, Matt Damon, Arnold Schwarzenegger.