Need help finishing $650 gaming PC ! (First-time)

Hey guys,

I'm trying to build my first PC on a budget. Mostly I want something that will allow me to play Diablo III for sure !

I also want a machine that will do everyday operations without a problem.
I have zoned in a few parts that really seems nice with the newerf eatures of the year.

I am trying to make it so that I will be able to upgrade to newer things and not have it become a "Prehystoric PC" in the
next 2 - 5 years...technology moves too fast sometimes lol

Regardless, here the parts I want on my system:


CPU: Intel Core i5-3570K Ivy Bridge 3.4GHz (Correct me if I'm wrong, but seems to be a great one)

http://www.newegg.com/Product/Product.aspx?Item=N82E168... $250


MOBO: BIOSTAR TZ77XE3 LGA 1155 Intel Z77 (Seems promising for a good price, with lots of features)
http://www.newegg.com/Product/Product.aspx?Item=N82E168... $120


GPU: Radeon HD 6850 (I have heard it's the best for my price range)

http://www.newegg.com/Product/Product.aspx?Item=N82E168... $140

Total so far: $510

I'm clearly missing other things like the Case, PSU, HDD, RAM, Coolers, and CD/DVD.

I mainly need help because I don't know what to choose, and I wanna make sure my system doesn't over-heat.
I don't understand anything about what a good case has, PSUs, and Coolers, and I don't need that much spare. I have 218 GB
on this laptop, and I still have 174 GB left.

The reason this is difficult even though there is A LOT of information out there, is that I do not want to give up on parts
that directly affect performance, such as the cpu, gpu, and the motherboard (for later upgrades)

My total budget is $650 after rebates, maybe $700 before rebates TOPS.

Please help me finish my first project with a $150 ~ $175 budget !