A few tips:
1) Don't buy a third party memory card unless it does something special(I only know of 2 of these, and they do the same thing-allow you to put gamesaves into your computer. If you find one, get it, but otherwise, stick with official Nintendo ones)
2) I actually prefer wired controllers to Wavebirds. In Super Smash Bros. Melee, I don't want a Wavebird messing me up. The wired ones are cheaper, too.
Get a memory card 251(official one is black) if you plan on getting more than 5 games. The Memory card 59(grey) fills up too fast. The memory card 1019(white) is infinite, there is no way you could ever fill one up*
*you're results may vary if you're a diehard Gamecube fan
3) You have to buy Super Smash Bros. Melee. No matter what. Otherwise you might be a target of Nintendo fanboys who are also assasins.
Other good, cheap games(
* denotes must-have):
Animal Crossing(even if you hate it, it comes with a memory card 59 for only $5 more than the cost of one, with a free game!)
*Timesplitters 2(Awesome multiplayer)
*Super Monkey Ball 1 or 2(Get 2, and if you like it, get 1)
Pikmin
List of what some people call good Gamecube games:
http://wiki.cheapassgamer.com/index.php/GameCube