www.modchip.ca Is were to buy a modchip (only $60) For people in US and Canada.
Xecuter 3 is currently the best modchip on the market today and has the most user support (especally in the forms)
I've been part of the xbox modding community for about a year and any questions you have about the xbox or modding it I will be happy to answer. (just PM or e-mail me.)