Also,
www.Pricewatch.com - a site of lists. select the component you need and it will give you a list of retailers that sell it in price order from lowest to highest. I've built 75% of all my machines using nothing but pricewatch, and everyone here has used it at some point.
www.Tigerdirect.com - whenever i need a well priced motherboard+cpu combo, this is who i use. I'm native to miami where they're located and go to the warehouse to save on shipping, but they have some of the most renouned combo's and barebones systems to start your project if you need a jump off point. They deal strictly in OEM components (if you don't know what that is, ask and we'll be happy to explain it), but are neweggs best competition and equally as renouned as newegg. again, everyone here has sourced things from them before.