Just Buy some xbox live points or buy a downloadable game code from amazon there are alot of 400point (5$) games
here some just to name a few
doom
marble blast
mortal kombat 2
Small Arms
Zuma
Assault Heroes
Geometry Wars Evolved
UNO
tnmt 1989
Golden Axe
Streets of Rage 2
GALAGA
Assault Heroes
DIG DUG
Gauntlet
Jetpac Refuelled
Joust
MS.PAC-MAN
Robotron: 2084
Sonic The Hedgehog
Sonic The Hedgehog 2
Ultimate MK3
Worms