As for processor I personally own a Phenom II X4 965 which is essentially the same thing with a slightly smaller multiplier and it runs very very fast but to be honest that was only because I already owned an AM3 motherboard. Starting from scratch I would recommend the 2500k for only $50 more.
As for the Motherboard, you're stretching yourself pretty thin with only an $80 budget. I found a decent one on tigerdirect for that price but it has very few bells and whistles. You get what you pay for. If you could allow yourself even $30-$40 more you could get much better quality.
The 6770 is essentially a rebranded 5770 which I HAVE owned and it worked very well. It will play most everything you need it to unless you want ultra hardcore settings at 1980x1200 and still expect 75 fps.
I currently own a 6870 which isn't too far off from the 6850 and in my opinion the difference was worth the money, so it's up to you on the graphics card, either is a solid choice.
For RAM, for $75 there's not much place to go wrong. Just brand suggestions you can get a good amount of G-skill or mushkin, or anything else really as long as you go DDR3 and personal suggestion at least 1333Mhz
You'll have yourself a respectably solid build with that. But once again, if you can at all, try to give yourself some more breathing room motherboard wise. You get what you pay for