well i do not know what type of games you are into playing so i will make a few suggestions on games that i personally like. For the GBA i would recomend Final Fantasy 1&2 Dawn of souls, or Final Fantasy Tatics Advanced. FF 1&2 is awesome if you have never played them for the NES than i would really recommend it as an awesome RPG. If you are more into strategy or tatics games then i do not think you could go wrong with FF Tatics.

For Game Cube i would say that my favorite games would be Super Smash Brothers Melee, for a good beatem up game, not overly complicated moves or combos just some good old fashion button mashing fun. If FPS games are your Genre i could whole heartedly recomend Metriod Prime. I have yet to play another game that has as nice of level detail in it. I have not got a chance to play the Second Metriod Prime game Alter Echos, but if it is anything like the first one you couldnt go wrong with it either.

For PS2 i dont have anything that really comes to mind as an outstanding game. Since you are going to get GT 4 then you do not need GT 3 which i thought was a superb game, with awesome graphics. I personally think if you have played any of the Grand Theft Auto games that there really is not a need to get a new one because they do not up grade the graphics at all they only add more weapons and different cars to drive around, but if you have not played it before you might pick up a copy of one of them for cheap.