Well, you could just buy all the things, buy a cheap processor (Athlon II X4 640) and wait for the Bulldozer to come out.
I'd suggest, right now, out of my head (for that budget):
1) ASUS Crosshair V Formula or Gigabyte GA-990FXA-UD7 (both AM3+)
2) 8GB (2 x 4GB) DDR3 1866MHz Mushkin or Corsair
3) Crucial M4 SSD (OS and apps)
4) Corsair AX Series PSU, could be 850W or 1200W (depending on your GPU configuration)
5) GPU (i'd change your HD4850) and buy 2 HD6950s (unlocking them to HD6970s)
6) 1TB or 2TB drives (data storage)
7) Blu-Ray Burner (can't tell you brands, cause i don't know too much about optical drives)
and you'll have money left for your Bulldozer
NOTE: the GPU i'd change it because the 4000 series doesn't have support for DX11, they're more power hungry... hell, i'd even wait for HD7000 series to come out haha. but that's your choice.