Russell Crowe is a way better choice than Javier Bardem IMHO. Crowe is much more rugged (the movie 300?!) I keep thinking about Bardem in Vicki Christina Barcelona and getting a tad grossed out! I think Crowe has more of an innate sense of Roland's character.
I was thinking of Gerard Butler! Who I actually can see as a gunslinger over Crowe, but that's probably because I'm a fan. I agree that Crowe would have to be much leaner to pull off Roland's character.