Disclaimer: I don't know much about hardware, so take these comments with a grain of salt.
I have had good experiences and have a good opinion of Dell. I have have bad experiences getting computers through EBay, and Dell's prices are comparable to what I can find on EBay anyway, and much easier to deal with.
Also, I haven't tried computers from Micro Center, but if you'd prefer to get a computer from a store rather than mail order, you might want to see if you have a Micro Center in your area:
http://microcenter.com/They have pretty good prices on a wide range of technology including desktops and laptops.