Some obvious choices but:
Johnny Depp - class act and a decent type of bloke to boot.
Robert De Niro - just plays himself usually but still damn enjoyable to watch
Dennis Hopper - about as good as it gets
Other less obvious ones:
Cameron Diaz - mostly because of her role in Being John Malkovich which was that good I didn't even realise it was her
Ricky Gervais - not really considered a top actor I suppose but his performances in the Office and to a lesser extent Extras were up there with as good as anything I can remember