I've been playing this free online FPS game. The initial download is available as a CD with Maximum PC this month, but the whole thing is available for download from the website:
www.warrock.net
The game is pretty good (for my inexperienced ass), there are 5 different characters you can play for free. I'm not sure how the pay side of it works, I've only been playing for free this week. There are a number of different maps and vehicles for every map, from humvees to tanks, F-16's to Warthogs.