Team Fortress 2

I used to love playing Team Fortress Classic. The Control Point matches were hillarious, with engineers' sentry guns just mowing down tons of people at the choke points, along with all kinds of grenades killing everything in the tunnels (the game had extra ammo you could pick up, sometimes giving you more nades).
This definitely needs to be on our group's to-buy list when it comes out, bundled with Half-Life 2: Episodes. There used to be a guy on the server I played on called Dr. Death. Of course, he usually played a medic, and went around infecting the other team....
One of the funniest moments was playing a capture the flag game, and waiting in our base for the other team to come capture it. We wondered what was taking them so long...until an entire team of heavy weapons guys showed up, with their gatling guns mowing down everything....