one thought about the CPU - a 3800 might not be your best bet, especially if you want to overclock. They use 130nm newcastle cores, and don't OC well - 2.5GHz is usually the max. On the other hand, lower end winchester cores (3000+, 3200+, and 3500+) OC much higher, 2.6GHz easy, some even hit 2.7-2.8GHz. They also run cooler when overclocked, and are cheaper to boot. And if you can hold off another few weeks, Venice cores will be here, and they'll OC even higher (initial estimates are around 2.9-3.0GHz, due to strained silicon), plus they have SSE3 and a better memory controller, than can handle 4 full DDR400 DIMMS. Either way, grabbing an old newcastle core is a waste of good money.
Everything else looks pretty good. X800XL is great, and the compusa seems like a great buy, although it's kind of a bummer there's no dual DVI, but that's probably just my personal hangup. With the PSU, make sure it's 24-pin, aka EPS12V, aka ATX2.03. Vantec, Antec, OCZ, and Enermax all make good 24-pin PSUs. They are important to provide enough power for a PCIe GPU. Kingston memory is decent, but Corsair is better, and their value ram is like $90 for a gig right now. It doesn't overclock great, but if you have lots of memory dividers, you'll be fine. Oh, and one last thing, for the HDD, i strongly recommend the Diamondmax 10 drives. The 250GB one is like $140 online, and it's fast as hell (16MB buffer and NCQ help out with this), plus it's quiet. In fact, I got a 300GB one for $140, so you might find a good deal there.