[B]This page[/B] shows the memory that DFI recommends for this board if you are going to overclock it. Even if you don’t plan on overclocking, these should be stable for you. If no overclock, then all you need is the DDR2 800.
G.SKill, Crucial and Corsair are all good choices in my opinion.
Be sure your power supply is from a good brand. This isn’t a part you want to skimp on, and going just by wattage isn’t a good plan. Seasonic, Corsair, PC Power and Cooling, and Fortron Source all sell good power supplies.
For such a nice machine, I would think an Nvidia based 8800GT would be the least capable card you might want. If you prefer ATI, then maybe a 3850. There are better, more expensive cards out there, but these will play the vast majority of games that have been released. Crysis is the only one that will really slow these down, and it puts a hurt on most anything if you turn on all the features.
For sound cards I’ve heard some good things about the Asus Xonar series, but they are quite expensive. Newegg has them, and the baby of the series is $89.99