Me, considering I strongly dislike Windows Vista and Windows 7, but I'll be getting an Radeon 5870 anyway, I've decided.
So the CPU (Phenom II 965) and GPU are set, I'm good for those - I just need to figure out what PSU, mobo, RAM, HD, fan, case, etc to buy.
Thanks for the replies BTW guys.
Edit: Just checked those whirlpool links, thanks dude - quite helpful.
Once DX11 is released, I think there'll be even less support for DX9, so whilst Vista/7 are gay, we might need them to continue playing games.
Regarding PSU/HDD/Case/RAM, the whirlpool configs are good as they make sure there's no obvious bottleneck and there's a core focus of gaming. They recommend a rather cheap but reliable PSU ($66 isn't too bad).
Case/PSU: The case is really subjective. It's just got to fit everything in it. A better case will be spacey, quieter, cooler (better airflow). They recommend a Lian-Li case. I think a lot of their cases look like they're about to transform and break your house, if you want something more professional/basic you can go for Antec cases. The Sonata III is a Case/PSU combo from Antec which should have a good enough PSU in it and is supposed to be relatively quiet. Up to you though.
HDD: Whatever your needs are. If you're not "legally" acquiring movies and not buying every single game that comes out then 500GB to 1TB is enough. The sweet spot right now in terms of $/GB is about 800GB and so getting a 1TB is fairly worth it. If you do plan on having a lot of movies/tv shows/music/games then get a 1.5TB or even 2 separate 1TB (like $30 cheaper than buying a 2TB drive).
RAM: Stick with the recommended one " G.Skill-Ripjaws 4GB DDR3-1600". It's got a fairly high speed (1600 MhZ) and should do the job.
MOBO: Unless you plan on overclock or doing SLI/Crossfire or something, the one suggested is basic and works well. " Gigabyte MA785GT-UD3H $106"
Fans: The CPU comes with a heatsink + fan already. Unless you want to overclock, this would be more than fine unless you live in Alice Springs or run your computer in a sauna. Also, the better cases usually come with a fan or two.
DVD drives: They're all the same, this technology peaked/plateaued a while ago so they're all the same.
Peripherals: Have you thought about these? Are you after these? The recommended peripherals are pretty decent.