
Mine:
Half-Life: Crowbar - OK, who doesn't love this weapon? Whacking headcrabs with this melee tool is a classic

F.E.A.R: Nailgun - Am I the only one who got a huge grin on my face the first time I nailed an enemy to a wall? I think not! Of course this weapon would be nothing without the great physics engine Monolith developed but nevertheless, an awesome weapon!
Alien VS Predator 2: Minigun - Letting loose down a hall filled with aliens, screaming "EAT THIS YOU WANKAH!" has never been as sweet as with the minigun. Once you start shooting you never want to stop

Half-Life 2: Gravity gun: Death by toilet. 'Nuff said.
All I can think of so far, list yours ^____^