The latest addition to my geek family is this. I wanted a computer that was super powerful, but also fairly portable. I liked some of the fragboxes that I've seen, but the cases are still too large (I first looked at building this with the Bitfenix Prodigy, which looks amazing but weighs 17 pounds for the case alone!).
Then I found the Coolermaster Elite 120. Everything else fell into place, and on Black Friday, prices bottomed the out, and I pulled the trigger.
Case: Coolermaster Elite 120. $50 from a local computer store.
Just over 7 pounds. Very small form factor, yet with enough room to handle the largest GPU on the market, AND accommodate a large, modular ATX power supply. Kind of a less attractive case, especially compared to
this, but with the weight consideration, this was the only case that had high ratings and was cheap enough to make it worthwhile to pursue the build I wanted.
Processor: Intel Core i3-3220 3.3GHz Dual-Core. $99 from Tigerdirect.
Cheap, fast as , and most importantly, the dual core doesn't generate much heat, really important for a compact case such as this.
Motherboard: ASRock H77M-ITX Mini ITX LGA1155 $94 from Newegg.
Reliable, cheap, reputable company and the needed Mini ITX form factor.
RAM: Mushkin Blackline 8GB (2 x 4GB) DDR3-1600 Memory $25 Newegg BF special.
SSD: OCZ Vertex 4 128GB 2.5" Solid State Disk $75 Newegg BF special
One of the fastest, highest rated SSDs.
GPU: VisionTek Radeon HD 7850 2GB Video Card $150 Newegg BF special (free Far Cry 3)
I admittedly took a risk here. VisionTek is a new company so they really haven't been evaluated, but the price was right, and so far they have great reviews. Far Cry 3 for free was huge as well since I wanted the game anyway.
PSU: SeaSonic G 550W 80 PLUS Gold Certified ATX12V / EPS12V Power Supply $55 Newegg BF special.
Gold certified is amazing at this price. I got a of a deal here, and it's got solid reliability ratings.
Blu Ray: LG UH12NS29 Blu-Ray Reader, DVD/CD Writer $50 from local computer store.
I wanted the flexibility to watch Blu-Ray movies. Admittedly I could have gone without this.
Total cost: $600 before tax. Shipping was free on everything except 1 or 2 of the items, so that was a nominal cost.
Pics:

Upside down PSU, lawl.

Evo LTE for size comparison

vs. Mid ATX tower. (If you're wondering I use the fruit by the foot box to store rogue socks until I can find their partner)
Review: When I first got it I was wondering if the performance would be up to standard. After testing and using it for a while, I've had to talk myself out of selling my desktop a couple of times. It's that good. It won't max BF3 or Metro 2033, but almost every other game I can set to 1920x1080 and crank everything up to the highest level possible and I get 50+ fps. The case is so small it actually fits in my
Chromebag and the pockets can store all the cables, etc. Temperatures are great across the board, although I mounted the power supply upside down so that it blows out of the case instead of down onto the processor. GPU runs fine temp wise, and the processor goes from ~40 idle to ~60C under load.
If you can tolerate the cable management portion, I highly recommend building something like this. All together the system weighs ~16 pounds. Easily carried, although obviously I have to bring a monitor with me as well. Small price to pay for the power and flexibility compared to a laptop.