For RAM, I would suggest you get 2 of these instead of that XMS:
Thats GREAT RAM!
Power Supply....I would get one with at least 500Watts...especially since you have a 6800 up in there.
Hard drive, Seagate barracuda is a great series! Although its SATA150 which your motherboard is compatible additionally with, but SATA II is faster! So this hard drive is great, cheaper, and faster! And most of all compatible!
Great hard drive, the samsung spinpoint P is what I have, VERY quiet.
Other than those things, this PC looks nice! Although I believe you are using stock AMD Heatsink and fan. In that case, don't use the thermal pad and use some arctic silver 5, the best thermal paste on the market:
Also, that will build you a great computer. You will probably want some case fans. And if you want the case inside neater and betetr airflow i suggest using rounded IDE cables.