I'd get the Western Digital 640gb. It's really fast, and a couple hundred $ cheaper! Check out reviews around the web.
I'd get at least a P45 with TWO PCI-E 2.0 16x lanes for your motherboard. Both will run at 2.0 x8 speeds, but that should be enough for two 4850's in Crossfire (if you want to add a second one at some point). FYI though, it's heavily debated right now whether or not 2.0 x8 will actually bottleneck 4850/4870 cards... Tweaktown seems to think so. So if you plan to Crossfire for sure and have the cash, x38/x48 may be the way to go.
Xigmatek heatsink if you plan to try overclocking the processor - which you should definitely do! It's pretty easy to get to 3.2Ghz with DDR2-800 memory.
Samsung 22" 2253BW has a 2ms response time. Best gaming LCD out there right now IMO.
Good luck!