Most cabinets support both ATX and uATX.
At 12-15k, you can get a very good AMD config too.
AMD Athlon II X2 240 @ 3.4k OR Intel Dual Core E5200 @ 3.2k
Gigabyte MA-78GM-US2H @ 4.7k OR Gigabyte G31-ES2L @ 2.5k
2x2GB DDRII RAM Corsair @ 3-3.5k (Comes with RAM Heatsink and is very good quality!)
OR 2x2GB Kingston DDRII @ 2.6k
9600GT 512MB Palit @ 5k OR ATI HD 4670 1GB @ 4.7k
I suggest you get the AMD config! The motherboard comes with HD3200 onboard graphics which is very decent. njoy!

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UPDATE: Gigabyte MA78GM-US2H is available for 4.5k now!