I would get a Corsair 850W Modular PSU, they are great, I am going to be getting one of them.
I wouldn't get a 280, although you can go for it, but you may probably want to go for the 5870, at around $150 extra, it's so much faster than the 285/295, and it has DX11.
And by God's name, make sure you get those Western Digital hard drives you say are going to get. Seagate suck.