The only thing I can think of to fit into your budget is a H61 board and 2300 SB cpu. You wouldn't be able to o/c and no dual vid cards, but it would be solid and fit in your budget. I'l post on on here in a bit.
With a budget of $850 I can post a 2500K build that will push dual 6870's or dual gtx 560's and include Windows 7.
omg my english sucks, ok i have an ssd 60gb, monitor 21 full hd, blueray player and a motherboard a785gm-ad3 for free brand new from a friend, im thinking of getting a 500 - 600 system that can support an Sli or Crossfire, and i will get the video cards later.,
my other question is, that motherboard the a785gm-ad3 esc blackseries, is it good for something? my friend told me is really really old.
the H61M boards won't do any overclocking at all, and lack RAID. the official spec lacks SATA 3 and USB3, but the model I posted hs 'em. They usually only have 2 memory slots. all have a single PCIe-x16 slot, so no Crossfire/SLI at all. Its a bargain basement board in terms of features compared to H67, P67, or Z68.
But, if you aren't going to overclock, aren't planning a RAID array, and only plan to use one video card, it really isn't that great a hardship, and saves you money toward a more powerful video card