"Tombstone" is one of my all time favorites! Great score. Great acting. And still reasonably historically accurate.
I think Tombstone is Cosmatos' best film, much better than anything else he did, in fact, although Rambo is reasonably entertaining. I see that film as being a more commerically- and action-oriented version of Taxi Driver, as it makes more sense if you view it as being the dream of the lead character instead of the depiction of actual events.