Actually, they don't work on GTA IV. I just tried mine, it said, "This code cannot be applied to this order."
EDIT: Nevermind, I guess it did work. I'll post some codes soon as well, be ready!
Here's some codes, please post if you use them (you too, lurkers!). I already used one of them, but I'm not sure which, so try not to pick that one
[FONT=verdana,arial,helvetica][SIZE=-1]PHZX-YCRH9C-U7CLEP
[/SIZE][/FONT][FONT=verdana,arial,helvetica][SIZE=-1]PHWM-EPM7KJ-S45747
[/SIZE][/FONT][FONT=verdana,arial,helvetica][SIZE=-1]PHX4-PUFFGF-BH8EQG
[/SIZE][/FONT][FONT=verdana,arial,helvetica][SIZE=-1]PHG4-ZLL6RT-KF4UJ5
[/SIZE][/FONT][FONT=verdana,arial,helvetica][SIZE=-1]PHR9-PMHH45-BFXZ2H[/SIZE][/FONT]
[FONT=verdana,arial,helvetica][SIZE=-1]PHHX-GC8RXN-MDZTGB[/SIZE][/FONT]
Here's a list of games you can use them on.