Totally, I'm building one myself as a GPU rig as well as future support for ASIC devices whenver they ship out (im in the queue).
Once ASIC power gets cranked up GPU mining will start dying as the difficulty will increase dramatically. Though, Litecoins and other Bitcoin derivitives are still in GPU stage, so you can mine something else too. LTC is cheap right now, but imagine if someday it grows to where Bitcoin is now riding the coattails.
My rig is as follows, all in all coming in for around $800 so far not including a case (building that myself)
http://www.blockburner.net/garden-party-bitcoin-mining-rig-build-begins/ -
Motherboard
GIGABYTE GA-990FXA-UD3 AM3+ AMD 990FX SATA 6Gb/s USB 3.0 ATX AMD Motherboard
I chose this board as the price point was decent, fairly solid brand, and can accept 4 full size PCI-x16 cards for future expansion.
Processor
AMD Sempron 145 Sargas 2.8GHz Socket AM3 45W Single-Core Desktop Processor SDX145HBGMBOX
Nothing too special is needed here, as the CPU won’t be doing a whole lot in terms of block crunching. I can still be viable to generate a little extra Litecoin cheddar though, but GPUs are still better at it by far.
Memory
G.SKILL 2GB 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600) Desktop Memory Model F3-10600CL9S-2GBNT
Again nothing special, 2gb should be just fine to let the OS breathe deep.
Power
SILVERSTONE ST85F-P 850W ATX 12V v2.3 / EPS 12V 80 PLUS SILVER Certified Full Modular Active PFC Power Supply
This beast should allow expansion to run all 4 graphics cards eventually. Just as a computer builder, it is never a good idea to skimp on your power supply.
HDD
I wanted to run this thing from a flash drive, it cost about $8 for an 8gb stick, and is so generic I’m not going to bother to look up the exact one I ordered.
Video Cards
So far, 2x Sapphire Dual X 7850s were ordered just today for a hashing capacity of around 600-700 MHash/s, eventually Ill add 2 more to up to around 1.5 Ghash/s