MWave Online Store
Mwave offers MB/CPU combos and MB/CPU/RAM combos. For $9 extra, they will install your CPU, your heatsink/fan with thermal grease, and your RAM and pretest it for you. Great line-up of products, very good pricing, reasonable shipping, and super customer service.
They might be a couple of dollars more than ZipZoomFly or NewEgg on some things, but if you have to RMA something they're great to work with. The $9 for assembly and testing is well worth it, too. I've bought several motherboard combos from them this way and never had an issue after they've tested it.