Even though Foxy has linked you to multiple pages describing excellent games, I will have to give my recommendations.
1.) Sonic Adventure 2-not big among the press, but I enjoyed it overall-just don't go into it expecting Mario 64, think Mario Sunshine
2.) Marvel Vs. Capcom 2-hard to recommend because unless you pirate it (which is lame, yo) it is going to be pricey when you find it
3.) Rayman 2 is an excellent platformer if you don't have it already
4.) Power Stone 1-2. Excellent fighter, fun with friends