What qualifies as a "gun battle"? Because personally, the gun battles in Indiana Jones 1 and 3 were/are my favorites, in part due to how they fit so seamlessly into the films. Not entirely realistic, for the most part, but certain things are likely as they'd take place in real life (at least in microcosm).
Indy 1:
- The ever-famous sword slayer slaying
- The 'intro' gun fight in Marion's bar
- The
Indy 3:
- "I told you, don't call me Junior!"
- The 'straffing fighter downed by birds' scene
I see a gun as not the end-all, be-all, and but a tool, secondary to the mind. Shoot-'em-up scenes can be entertaining as all getout, but that isn't entirely what makes the scenes entertaining: it's the one-upsmanship of the good guy over the bad guy using superior skills and utilization of weaponry.
The sniper battles in the second half of in Enemy at the Gates were awesome.
Also, Heat and Ronin had some awesome gun battle scenes.
ETA: Oh man, can't believe I forgot The Professional! Awesome gun scenes at the end. If you rent it, make certain you get the "director's cut" version: it's not only a good action film then, but an awesome piece of cinematographic storytelling.