Where to buy bicycle parts online?

[sammypetter]

One of my friend recently got into mountain biking a bit, and am wondering if anyone knows of good online stores from where he can buy to upgrade his bike. There seem to be very few stores that sell online, even on eBay. So far, Cyclepath and Mountain Equipment Co-Op are the only places I found selling parts online.

Does anyone know of any other retailers that sell bike stuff online?

Thanks in advance!