If you want an SFF case that will take a full ATX mobo, you might want to check out the Silverstone LC02. It will take a full ATX mobo, but there are several caveats:
- To use both one AGP and one PCI slot, your mobo must have the AGP slot in the A-position and a PCI slot in the B position.
- You must use a laptop-form-factor slimline optical drive.
- You need to use a good, short CPU cooler.
Ain't cheap, but after making the investment myself, I have an HTPC in a very nicely-styled aluminum case that is only about 12 inches deep, 5 inches high, and 15 inches wide. With a full ATX mobo inside.
HTH.