+2 on what the guys said. You should really look as to what kind of mods you plan on and work from there. I would start on the mods like intake, exhaust, headers or what not. Then work on the chip. The chip I have is custom made that I got from a good friend, and coupled with some changes I did on the drive train also, I have been able to up the overall output of the car itself.
Also, when you go for the chip, get one that is worth the money and that you feel that will deliver what you want in terms of power output.
Oh, and the final rule, DON'T GET A CHIP ON EBAY!!!!!!