Your CPU is quite out of date. AMD has officially stopped supporting the AM3 and AM3+ sockets now. They're only supporting AM1 and FM2+. That will make the PC very hard to upgrade and will keep performance lower than it has to be.
These would be my suggested revisions, which would increase performance and make upgrades later easier.
PCPartPicker part list /
Price breakdown by merchant /
Benchmarks
CPU: AMD Athlon X4 750K 3.4GHz Quad-Core Processor ($79.18 @ OutletPC)
CPU Cooler: Gelid Solutions CC-TranQ-01-A 58.0 CFM CPU Cooler ($35.98 @ OutletPC)
Motherboard: ASRock FM2A75M Pro4+ Micro ATX FM2+ Motherboard ($59.49 @ Newegg)
Memory: A-Data XPG V1.0 4GB (1 x 4GB) DDR3-1600 Memory ($42.99 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($54.44 @ Amazon)
Video Card: Sapphire Radeon R7 260X 2GB Video Card ($114.40 @ Newegg)
Case: Silverstone RL04W ATX Mid Tower Case ($44.99 @ Amazon)
Power Supply: EVGA 430W 80+ Certified ATX Power Supply ($34.99 @ Micro Center)
Optical Drive: Asus DRW-24B1ST/BLK/B/AS DVD/CD Writer ($16.99 @ Newegg)
Case Fan: Antec 75024 79.0 CFM 120mm Fan ($8.08 @ OutletPC)
Other: Rosewill RNX-G300LX Wireless Adapter Card ($10.99)
Total: $502.52
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-05-08 00:40 EDT-0400)
Also, people might recommend an FX-6300 instead, but I wouldn't go for it. The AM3+ socket is sort of a sinking ship, and the cost is too much higher to justify the bit of extra performance.
Anyway, as you can see, the Athlon runs better than the Phenom II you were looking at and the FM2+ socket means you'll be able to keep the motherboard longer.
http://cpuboss.com/cpus/AMD-Phenom-II-X4-945-95W-vs-AMD-Athlon-X4-750k
The R7 260X performs better than the HD 7750 and is newer/more efficient, but if you want to keep the price lower than the 7750 is still a pretty good choice.
http://gpuboss.com/gpus/Radeon-R7-260X-vs-Radeon-HD-7750
As for a case, your case is ATX and your motherboard is mATX. They'll still work together fine, but if you wanted you could get a smaller case to save space. Or you could stick with the case you already chose, if you like how it looks.
Finally, you only need the CPU cooler if you plan to overclock. If you're not going to overclock the CPU, you don't need the cooler and can save some money there. CPUs come with their own small coolers that work fine unless you overclock.