Nexuiz - Open source FPS.
7-Zip Archive Manager - Open source file archiver, a fantastic alternative to Winrar and Winzip. Mostly because it gives you the features that those two require you to pay to use, on top of supporting a better archive format.
Democracy Player - Think of it like a version of TiVo for web-based video. That's a gross oversimplification, but y'know. It's great. Note that they're changing the name soon, with the release of 1.0.
Urban Terror - A TC of Quake III Arena, now completely free to play for all using the recently GPL'd version of the Quake III engine. It's super fun.
Battle for Wesnoth - Open source tactical turn-based strategy game.
Ubuntu Linux - Free operating system. No strings attached. Lots of free software pre-installed and the ability to install even more free programs. 99% unlikely to get you viruses, spyware, adware, or hacked. Won't steal your soul (unless you want it to)