I go on craigslist and ask people who are selling a system with games if they would sell just the games for x amount.
A few times a buddy and I went halfers on a whole bundle including controllers, wireless adapter, charge kit, and games. Cost each of us about $110 but we each got 4 games, a wireless controller with a plug and play kit. I took the dual control charger and he took the wireless adapter. Worked out for both of us. I've had my 360 for about 2 months and have almost 30 games now. My most recent additions are Kane & Lynch and fallout3. This weekend I will be buying MK vs. DC universe for my wife's benefit.