First build compatibility

Hello, so I saw a post by proximon in regards to building a gaming computer and I really liked their build. I'm excited by the prospect of building my first PC and wanted to pick the forums collective brain(s) to see if the parts below would be compatible. Here is what I am looking at based primarily off of proximons build suggestion:

CPU: Intel Core i3-2120 Sandy Bridge from amazon

MoBo: ASRock H61M/U3S3 from amazon

Ram: Wintec Value 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3

GPU: SAPPHIRE Radeon HD 6850 -newegg

HDD: Western Digital Caviar Blue WD5000AAKX 500GB 7200 RPM -tigerdirect.com

Case: Cooler Master Cooler Master Elite 430 Mid Tower ATX Case with Window

PSU: Corsair CMPSU-500CXV2 Builder Series™ CX500 Power Supply -tigerdirect (nice mail in rebate now)

optical: ASUS 24X DVD Burner -newegg

OS: windows 7 -Amazon (seems to be 99.99 pretty much across the board)

Since its my first build I was just a little concerned that I may be leaving something out or that something wouldnt be compatible.

Primarily I plan to use this for gaming (Diablo 3, league of legends), internet surfing, and microsoft office type use. According to my tally it all comes to about $635 which is about $80 more than proximon's original build but perhaps some of the sales have expired? At any rate, i'd really appreciate someone taking a look at this and getting your feedback on it!

Thanks in advance to anyone who answers!