These games prove the critics don't know jack when it comes to fun games:
Test Drive: Eve of Destruction...so many different ways to race (suicide, circle 8) and multiple variations of the demolition derby (how can you NOT love that), plus you can race SCHOOL BUSES!
NBA JAM: Maybe its the old schooler in me, but this game just does so much more for me than NBA Street 2....it's just a freakin blast to play (gotta love the dunk'o'licous, high-flying five point shots, except when its the CPU scoring them.
Yager: Yes the controls are difficult to get used to and some missions will bust your nuts, but once you play it for awhile the story and graphics will suck you right in (and it's only $10 at Best Buy).
World Racing: As long as you don't go off track and notice some of the glaring bugs that occur when this happens (driving through trees, the fugly water effects up close) the graphics are bright and colorful, the tracks are plentiful and creative and the racing is flat-out fun. Kinda reminds me of the early NFS games in terms of the creative tracks.
MX Superfly with Ricky Carmichael: Tracks are a lot better looking and creative to ride on then in MTX Mototrax or the other cycle game from Rainbow Studios which escapes me now and it can be had on the cheap nowadays.
Guilty Gear X2: Poor sales did not do this $20 gem any justice. It's the best 2D fighter on the Xbox to date.
Killswitch: Mindless? Yes, but boy is it fun in short doses to just blast away while shot dodging.
Rocky: The 1st one. Pure genius from the folks at the now defunct RARE (sniff, sniff). It's no Fight Night, that's for sure, but as far as an ARCADE version of boxing goes it's a lot of fun. Worth it to hear the Rocky song and see the likes of Drago and company alone.
As someone else said, so many good Xbox games to be had for cheap nowadays you'd be a fool not to add these suggested titles to your collection.