Any of the Intel mini-itx Atom boards should suit your needs. The D510MO is a good dependable board that requires little power. You can also check out the new AMD Fusion mini-itx boards. I have the E350M1 (well, it's at ASRock right now, getting RMA'd) and it also draws very little power. All mini-itx dimensions are the same, so those will fit in your case - but I don't know how high your case is, so that's something you'll have to check to make sure the board+processor will fit.