Rosewills are only good for goodwills, they suck. I've had 3 of them 2 of which burned out within 3 months. Even though its a house brand of newegg, they suck. Stick with the name brand stuff like Antec, Corsair, Seasonic or the cheaper OCZ, Cooler Master and Thermaltake brands that work just as good. For the same price of $50 you can most likely find a 550-650 watt psu easily.
As for the RAM, just get these: G.Skill 1600 cas9 2x4gb ddr3
While the i5 2300 is a decent chip, its only a few bucks more for the kickass i5 2500k, you can find them on sale around 180 or so, atleast it was last week. 200 most places now I guess. Well worth the extra 30 bucks.
In terms of the 6850, its a great card, good value for the money. Alternatively, you can get a gtx 460 that's about the same power for about $10 cheaper (125) although I just picked one up for $100AR last week at us.ncix.com. It's only 2-3 frames per second slower in most games at 1080p.
+1 for the CM 212+ CPU cooler, best buy. Alternatively the Corsair A70 is about the same thing for about the same price.
For a motherboard, stick with the z68 chipset, its the latest and costs the same as the older p67 but the z68 has a few new features, such as the SRT ssd drive feature. Not something that you'd use in your budget system, but its a nice feature if you do decided to upgrade to an ssd.
Also, for the same price, here's a 500gb 7200rpm hitachi drive
. They are a bit old but dependable. I've been running 4 of them in my 5 yr old gaming rig in a raid 5. $30, not to shabby.