i would suggest
broforce(fast pace side scroller shooter that is totally awesome)
total war series (best RTS ever i can run medevil 2 on huge scale setting with max graphics with a Pentium 3 + 4g's of ram and a shitty graphics card.) best imo are rome, medevil 2, and empire. rome II probably pretty good also.
dont starve (survival in the wild game)
the long night (horror survival game)
and eve online(space mmo)
also check this out. no drm
http://www.gog.com/