Again, if we are not talking serious racers here then the game I spent the most time with had to have been:
Rock'n'Roll Racing 
A great graphical style and awesome licensed soundtrack, fun characters (including a Lost Vikings cameo) and gameplay and a good challenge with plenty to unlock in the way of vehicle customization and upgrades.
It's also available as a GBA port which I hope to pick up someday. Sadly the licensed music might prove too costly to negotiate for a deserved VC release.