Go to newegg, they are by far the best in price and reliability for service and delivery, and returns. I have bought gobs of stuff from them over the years, have never been disappointed.
Newegg, and FRey's , PC CLub is where I get my stuff.
If you are not near a large Metro area, mail order is a good option, I have multiple Frey's to choose from here, so I go there first , but always check out things on the internet first.
BTW, if your just interested in getting memory, you might want to buy direct from Crucial, they have some of the most stable and solid memory out there, with a lifetime gurantee. There website has an easy to use configurator that will help you determine the exact memory modules needed by a specific pc. They also have free shipping.
http://www.crucial.com/index.asp