I watched Leon tonight, first time in ages. I had the house to myself, cooked a pizza, and put it on.
Thoroughly enjoyed it the whole way through. If anyone hasn't seen this film, I'd say you should check it out. Jean Reno is great, and so is Natalie Portman and Gary Oldman.
I think Leon is about the slickest hitman I've seen on screen – his modest, slightly simple character helps this immensely – and when he's doing his job you're left in wonder at his very slick way of killing people.
It's strange, I'm not one for hugely violent films, but I think you feel a certain amount of detachment from the killing in this.
If anyone else can recommend good hitman films I should watch, let me know!