NZFF

If youve ever wanted Quake 3, but dont have the money, check out this:
http://mods.moddb.com/5727/openarena/image-gallery/

Ive tried it and its awesome! Its got internet servers, lots of maps, and the same layout as Quake. The other great thing is its only 72MB! Do-able even by you dialup users

Another awesome free game is '.kkrieger' ( read about it here: http://en.wikipedia.org/wiki/.kkrieger )

It has awesome graphics, you play it offline but somehow it only uses 97,280 bytes of disk space!

Play it here http://www.theprodukkt.com/kkrieger