I realize you asked us not to comment on your CPU but I warn you that it will be a serious bottle neck on performance, especially in games. It might not be very bad with only a Radeon 6850 but it's still pretty bad.
You have to realize that FX processors are slower than the previous Phenom II processors and the Phenom IIs are three or four years old. That means that your CPU is outdated and slow as soon as you buy it, putting you at a severe disadvantage and making your machine significantly less future proof than even buying an older Intel Nehalem CPU would, let alone the newer Sandy bridge CPUs or the upcoming Ivy bridge CPUs from Intel.
AMD just isn't a high performance brand anymore, even though some of it's price tags make it seem like it is.
A 990FX motherboard is literally built for crossfire/SLI. You would have been better off getting a cheaper 970 motherboard instead.
I have heard that Gigabyte video cards aren't the best overclocking cards and that Asus, XFX, HIS are better.
For memory, I recommend a 2x4GB 1600MHz 1.5v kit, price should be around $30-45. Recommended brands would be G.Skill, Corsair, and Crucial. I have had and heard the least amount of problems from these brands. Other brands are okay like Patriot, Kingston, and some others but I have heard of many more problems with Patriot and Kingston than with G.Skill, Corsair, and Crucial.
Good thing about memory is that you often get life time warranties, no questions asked so they will be replaced for free if DOA, just incompatible, or if they die a few months/years down the road and will usually even be replaced if they were overclocked.
Since you went for an AMD CPU you will need to overclock it to get decent performance. To overclock it you will need a good cooler, I'd look for something with a cost of $40-60 for a good one that isn't too expensive.
You can look through the reviews on frostytech.com for a cooler you like and then look at it's price on Newegg.com.
Best gaming CPUs on AMD platform would be the quad core Phenom IIs, not the six cores.
The Phenom II x4 955 BE would be the best option, if you can find one. If not then go for the Phenom II x4 960T BE, it's easier to find. Actually, go for the 960T anyway. It might be unlock-able to 6 core (sometimes it works, sometimes it doesn't). If you have this machine a few years later and games can make better use of more cores then you can try unlocking it. If it works then you now have a free CPU upgrade when core count matters more (or is equally important) than performance per clock and clock frequency.
Remember, you would still need to buy a good cooler and overclock the CPU to get it fast enough but it will then be faster than any FX CPU.
The 960T BE is the only retail CPU that might unlock to a six core, the indicator for this is the T after it's number.
The T indicates that it has a six core die. It is sold as a quad core but it really is a six core processor with two cores disabled. if there is something wrong with the disabled cores then it won't unlock them but if they are intact then you can unlock them.
BE indicates that the CPU multiplier is unlocked. An unlocked multiplier can be increased from it's default to overclock the processor. It is the simplest way to overclock a processor but only works on unlocked processors.
BE or Black Edition Phenoms and Athlons have an unlocked multiplier. All AMD FX CPUs have an unlocked multiplier. K edition Llano CPUs have an unlocked multiplier.
For Intel's Sandy bridge, Sandy bridge E (E for enthusiast), Ivy bridge, and probably Ivy bridge E if such a thing comes out, all K edition processors have an unlocked multiplier. Intel started the K edition meaning unlocked multiplier first, AMD copied it for Llano and likely will for their next Trinity APUs that succeed Llano sometime in 2012 or 2013 (probably 2012). AMD likely copied the K edition naming for simplicity between Intel and AMD CPUs.