I'm surprised nobody has mentioned Paul Newman.

My list:
1. Paul Newman
2. Robert DeNiro
3. Tom Hanks

1. Newman - Arguably the best actor of my lifetime. He's been entertaining for the last 50 years and although most of his best roles (and my favorites) were from his first decade ("Cat on a Hot Tin Roof", "The Hustler" and "Hud") he's had some awesome performances in his later years as well ("Nobody's Fool" and "The Road to Perdition"). He's got style and charisma and just seeing his name in the credits is reason enough for me to want to see the movie. He's equally credible in comedy as he is in dramatic roles.

2. DeNiro - I don't suppose he needs any buildup on these boards but he's among the most exciting actors I've ever seen on the big screen. While I don't particularly like his comedic efforts ("Meet the Parents", "Analyze This", etc.) his dramatic roles overcome them and although he's at his best when portraying a gangster he's had some AWESOME other roles ("Raging Bull", "The Deer Hunter", etc.) He scared the shit out of me as Max Cady in "Cape Fear"!

3. Hanks - When he started out his career, he was often compared to Steve Guttenberg, another young actor in similar roles. I thought Guttenberg would be the one to make it big... boy, was I was wrong! Hanks has an uncanny ability for picking great roles and then going out and making them even greater. Whether it be "Philadelphia", "Forest Gump", "Saving Private Ryan", "The Green Mile" (my favorite) or "Road to Perdition", he's entertaining and totally believable in his portrayals.