#134
The i3-2120 is 2 gens old, 4th gen is current. I'd recommend an i3-4330.
No cooler needed, the CPU comes with one.
Different mainboard for a 4th gen (= LGA1150) CPU. Also µATX because smaller = cheaper.
Better and cheaper RAM.
Smaller case (see mobo), mostly a placeholder though, just take whatever you like.
PCPartPicker part list / Price breakdown by merchant / Benchmarks
CPU: Intel Core i3-4330 3.5GHz Dual-Core Processor ($134.98 @ SuperBiiz)
Motherboard: Gigabyte GA-B85M-DS3H Micro ATX LGA1150 Motherboard ($52.05 @ Newegg)
Memory: Team Vulcan 8GB (2 x 4GB) DDR3-1600 Memory ($64.99 @ Newegg)
Storage: Seagate Barracuda 500GB 3.5" 7200RPM Internal Hard Drive ($49.99 @ Best Buy)
Video Card: Asus GeForce GTX 660 2GB Video Card ($169.99 @ NCIX US)
Case: Silverstone PS08B (Black) MicroATX Mid Tower Case ($36.99 @ Amazon)
Power Supply: Corsair Builder 430W 80+ Bronze Certified ATX Power Supply ($34.99 @ Micro Center)
Operating System: Microsoft Windows 8.1 (OEM) (64-bit) ($89.98 @ OutletPC)
Total: $633.96
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-05-30 10:27 EDT-0400)
No USB 3.0 front ports means that you can't use the internal USB 3.0 headers. The USB 3.0 ports on the back will still work and there should be headers for front USB 2.0 ports too, so you'll just have USB 2.0 on the front panel.