CS:S Physics Fun
Counter-Strike: Source lets server admins determine how strongly a bullet's impact will affect the environment. Essentially, it is to shooting an object what low gravity is to jumping. Alter this variable, and stuff flies across the screen when you shoot it. It's incredibly silly, and I love it do death.
I recorded a demo of myself playing on a server with this setting altered. (You can't watch the demo without CS:S, sorry.) The server was a bit laggy and it shows in the demo, but you can watch some pretty crazy physics and vicariously experience my amazing headshot ability. Enjoy.