I really like the Saving Private Ryan scene where the German and American run out of ammo near the end of the movie and it's down to fists and eventually a knife. Very unnerving scene with foley.
I also like the new Bond fist fights.
But the one that I always loved was the fist fight between Indiana Jones and the super-huge bald German guy in front of the airplane getting ready to take off. The slap echoes Ben Burtt created for those punches were so unique that I pointed out to a friend that in the 4th installment (Crystal Skull) it sounded like they used the same exact punches, and they did!!
I'm surprised no-one mentioned the Mortal Kombat 2 punches! Those are the largest, most air-moving slams and hits I've ever heard (totally fake sounding of course, but they sound awesome)