I just wanted to recommend my build:
Basically I'm suggesting you go for the same case and similar hardware. The case can "only" mount 2x 2.5" HDDs though. (I think for this footprint it's already brilliant!) I should have posted a build progress thread but was too lazy back then. Currently waiting for Trinity to come out and I'll jump on it, but when it comes out I won't even have time for a casual game
Here's the build: (The prices were what I paid - Current total price shouldn't be too far off what I paid, RAM was a bit more expensive back then)
CPU: Intel Pentium G620 (£35 2nd hand)
Motherboard: AsRock H67M-ITX (£70)
RAM: Kingston Low Profile 8GB DDR3 1333Mhz CL7 (£50)
Storage: 250GB WD Scorpio Black HDD (~£34) + 64GB Crucial C300 SSD (£46 Refurb from Crucial)
Case + PSU: Antec ISK-100 with included 80W Pico-PSU (£60)
Total: £295!