as the are to many Jonny Depps, Bruce Willis and Nick Cages i will have to go with Samuel L Jackson, Hugh Jackman (Always in my sort of films), or John Travolta (Later films)
well people have already said al pacino which i agree with completely.
then i like mel gibson - we were soldiers was excellent
samuel l jackson
adam sandler - he continues to make funny films he must be good.
tom cruise - born on the forth of july was great.
Johnny Depp
Kevin Spacey
Tom Cruise
Also, the vastly under-rated Woody Harrelson. Doesn't seem to do many films these days (at least none that get a UK cinema release), but he's always excellent. See Natural Born Killers, The People Versus Larry Flint and Kingpin.
Once again-Johnny Depp! I had a dream last night I was getting married to him. Before he could say, 'I do' my mum burst in my bedroom at that point, waking me up, completely ruining it!!!!!!! Damn you, mother!
alan rickman - absolutely - great at playing the villain, but really good in something like love actually too.
not on the a list, but i think hugely underated i'd go for kevin bacon - for films like mystic river, stir of echoes, wild things, a few good men, apollo 13 and my favourite, murder in the first with christian slater.