Battlefield Bad Company 1&2: There have been several times where someone has been driving a jeep at me and I was playing Demo. Just whip out my RPG, blow the mofo up, and watch as the jeep perfectly flips over me and crashes to the ground as I walk away.

Resident Evil 5: "BAH, I'M CHRIS REDFIELD, smurf YOU BOULDER!"

Fallout 3: Lots of fun VATS kills that look badass, and then of course blowing up Megaton the first time was pretty sick. Also, Liberty Prime.

That's all I have off of the top of my head.