Sometimes I purchase items from this store:
www.directron.com
They build computers both AMD and Intel and sell parts as well as systems.
There are probably hundreds of competitors on the Internet that sell parts. Not many stores are as large as newegg, or have the selection they do. Often if you wait a while what you want or something just as good will go on sale at newegg. They not only have the best selection, but they have a good return policy. I like their pictures too.
On a side note if you want even more deals sign up for the Newegg newsletter. Sometimes they have extra savings but you have to get the newsletter and use the codes on there to get the savings.
If you like to assemble computers you might also look for the kind of case you want on youtube. They have all kinds of reviews of parts and cases on youtube.