well, for downloadable games, that are totally free, there is gunbound and gunz.
Gunbound is pretty neat, it is like the game tanks, but with other people, and you have animals and machines that have eyes, instead of tanks. The different vehicles perform different, and you can get money to change your avatar, which does things to your tank, like bigger blast radius.
Gunz isn't to fun, it is a glitchy 3rd person shooter, that tried to take cool moves like wall running, and hanging on the wall, but doesn't have that good of graphics. Same thing like gunbound, you can buy guns and clothes for your person, with in game points.
In both of the games you can use actuall money to get things, in gunbound you can only buy some garments with real money, but it is not required.