Hey guys. I'm going to be building my first computer. Since i've never built a computer, i have no idea on what parts to use with different parts. I have a list of parts im planing on using:

Power Supply: Crosair GS600 power supply

HDD: Seagate Barracuda ST500DM002 500GB 7200 RPM 16MB Cache SATA 6.0Gb/s 3.5" Internal Hard Drive -Bare Drive

Case: COOLER MASTER HAF 922 RC-922M-KKN1-GP Black Steel + Plastic and Mesh Bezel ATX Mid Tower Computer Case

CPU: Phenom II X6 1045T 2.7GHz Six Core Socket AM3 Boxed Processor

Motherboard: ASUS M4A77T/USB3 AM3 AMD 770 USB 3.0 ATX AMD Motherboard

And i can't decide between these three video cards: EVGA 01G-P3-1460-KR GeForce GTX 560 (Fermi) 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card
or
EVGA 01G-P3-1556-KR GeForce GTX 550 Ti (Fermi) FPB 1GB 192-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card
or
MSI N560GTX-Ti Hawk GeForce GTX 560 Ti (Fermi) 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card

I'm trying to build a more or less budget (budget meaning within $500) gaming computer. Nothing too serious. Minecraft, Amnesia, maybe a little left 4 dead. If anyone has any suggestions, that would be great (remember, budget pc that will play games on mid to high graphics). Thanks in advance.