Velocity Micro and Falcon Northwest are two more. I think they market themselves towards the gamer community and the more 'sophisticated' user (well, more than Average Joe), but I assume they could build any level of system you'd want. Last time I checked either site was about, oh, 9 months ago or so, but the impression I got at the time was that they would be considerably better than Fry's, Best Buy, or any of the other mass-production outfits where you're just a number. A computer configured and bought from those two sites I mentioned will cost you more, but prolly be well worth the extra $$ compared to Dell, Gateway, e machines, Best Buy, et al. They pay more attention to detail and offer better components.
Of course, the best thing to do is hang around these forums for a bit longer. It might not take long before you decide to take the plunge and build your own!
Hope that helps. BTW, pick up any established computer magazine and you will see at least a dozen ads from companies that do what you're asking about. PC Magazine, PC Today, PC World, CPU, Computer Shopper .... pick a mag, any mag.
