Here is what I play and what I recommend (google them, saying the name of the game and then "game", like Altitude would be "Altitude Game"):
Altitude
Gymnast
Toribash (this one takes up a ton of your time)
Smokin' Guns
Urban Terror
GeneRally (best racing freeware game ever)
Cortex Command
Gang Garrison 2 (Team Fortress 2 Demake)
Dwarf Fortress