AsRock Z77 Extreme4
Intel Core i5 3570K
Crucial M4 128GB or Samsung 830 128GB
Fractal Design Arc Midi, Fractal Design R4
You'll probably be wanting to upgrade the graphics card too in the near future.
If you have a Microcenter nearby you can get a significant discount on the CPU in the store if you buy a motherboard at the same time.
You will also probably need new RAM - something like Corsair Vengeance low profile, Mushkin Blackline Enhanced or G.Skill Ares would be what I'd recommend.
PCPartPicker part list / Price breakdown by merchant / Benchmarks
CPU: Intel Core i5-3570K 3.4GHz Quad-Core Processor ($189.99 @ Microcenter)
Motherboard: ASRock Z77 Extreme4 ATX LGA1155 Motherboard ($134.99 @ Microcenter)
Memory: Mushkin Blackline 8GB (2 x 4GB) DDR3-1600 Memory ($48.99 @ Newegg)
Storage: Crucial M4 128GB 2.5" Solid State Disk ($108.49 @ Adorama)
Case: Fractal Design Arc Midi Tower ATX Mid Tower Case ($109.99 @ Amazon)
(Prices include shipping and discounts when available.)
(Generated by PCPartPicker 2012-08-05 17:27 EDT-0400)
The alternative SSD:
Storage: Samsung 830 Series 128GB 2.5" Solid State Disk ($97.49 @ B&H)
The alternative case:
Case: Fractal Design Define R4 (Black Pearl) ATX Mid Tower Case ($109.99 @ Newegg)
Cases are very much a personal preference though. Remember, you're going to be sitting next to it for the next 4-5 years (or longer)
As for graphics cards:
Video Card: XFX Radeon HD 6870 1GB Video Card ($154.99 @ Newegg)
Video Card: MSI Radeon HD 7850 2GB Video Card ($237.49 @ CompUSA)