Here's my montage that I made ages ago (before Gears montages were popular):
http://www.youtube.com/watch?v=0Y-57IRZuS0
No crappy heavy metal.
Halo with Grunt Birthday Parties.
Max Payne with a sniper rifle...from the view of the bullet.
Unreal Tournament '99 / Unreal Tournament 2004
Accept no substitutes.
Gotta agree with Gears. The headshot pop sounded so juicy, especially when you used the Longshot.
Turok - Cerebral Bore
Resident Evil 4
Halo with Grunt Birthday Parties.
Soldier of Fortune II. Any gun at short range.