lucidrainbow :
Would the 5400RPM drive be a large problem in terms of boot times/load times/etc? I know the Phenom II x4 is great, though.
Yes, 5400 RPM is DRAMATICALLY slower than 7200 RPM. It's worth the extra five dollars. If you have the extra money, for ten dollars more I'd recommend the GTX 560 ti. It's almost as good as an HD 7850, and RAPES both the GTX 650 AND the 7750, and even the 7770. It's 93 dollars at NCIX US including a $20 rebate right now.
This is probably the best build you could get for your price range right now.
PCPartPicker part list:
http://pcpartpicker.com/p/myxP
Price breakdown by merchant: http://pcpartpicker.com/p/myxP/by_merchant/
Benchmarks: http://pcpartpicker.com/p/myxP/benchmarks/
CPU: Intel Core i3-2120 3.3GHz Dual-Core Processor ($109.99 @ NCIX US)
Motherboard: ASRock H61M-DGS Micro ATX LGA1155 Motherboard ($39.99 @ Amazon)
Memory: G.Skill NS 4GB (2 x 2GB) DDR3-1333 Memory ($19.99 @ Newegg)
Storage: Seagate Barracuda 500GB 3.5" 7200RPM Internal Hard Drive ($54.99 @ NCIX US)
Video Card: MSI GeForce GTX 560 Ti 1GB Video Card ($93.30 @ NCIX US)
Case: Rosewill REDBONE ATX Mid Tower Case ($32.00 @ Newegg)
Power Supply: Antec 450W ATX12V Power Supply ($35.83 @ NCIX US)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer ($15.99 @ SuperBiiz)
Total: $402.08
(Prices include shipping, taxes, and discounts when available.)
The i3 beats the Phenom in just about ever aspect, the Antec VP-450 is a better PSU than a Corsair CX 430,and 4GB is all you will ever need for gaming. 4GB sounds like a little, but it's been proven in numerous tests, so you'll be okay.