+1 to a single 6850. Always better to get a more powerful single card now. If you get two lower level cards, then when you want to upgrade you have to get rid of both of them. Definitely stick with the 955, with a cheap cooler like a Cooler Master 212+, you can easily get 3.6 GHz without changing the voltage.
Any PSU with a little voltage switch (e.g. that Chokemax) should be avoided if at all possible. A quality modern PSU has full range active PFC (no little voltage switch) and at least 80+ certification for efficiency. Antec, Seasonic, Corsair, Enermax, and XFX are among the better brands. FSP probably is too. If it has "max" in its name and isn't Enermax, the "max" is a reference to the number and expense of the parts it will take with it when it dies, or the size of the pyrotechnic display.
A single HD5670 will work well for your resolution, and not require a big PSU; 300W would be enough.
Phenom II x4 955 BE
Asrock 880 GM-LE(says it supports Crossfire and has a built in GPU Radeon HD 4250 graphics, can I crossfire it with the 5570 or 5670?)
Radeon HD 5570 or 5670 if I have the money, if not I'll buy it after a few months when I have it
HDD 500GB WD
2x2 GB RAM
The onboard 4250 can only crossfire with a very limited anount of low end cards, and most of the time, performance actually went down in games. I'm running a 5670 with a Intel Q6600 stock speeds and it plays everything at 1080p at least medium settings with no Anti-aliasing. But getting a 5770 if you could would be a huge increase over the 5670.
A quality modern PSU will have full range active PFC (no little voltage switch) and be at least 80+ certified for efficiency. Antec, Seasonic, Corsair, and Enermax are among the better brands that have products in the 380W-450W range that would be sufficient for you. FSP would also be decent. Sunbeam, Apevia, Coolermaster, and anything with "max" in its name other than Enermax will be junk. Antec Earthwatts models in particular are often sold around here for very good prices. I do not have access to the site mosox linked from work, so I don't know what brands are available to you.