I think for the most part any socket 939 PCI-E board will run any socket 939 CPU. The only problems I've heard of were BITD when dual cores first came out, mostly on older AGP boards. If in doubt, just make sure the board supports Winchester core Athlon 64, since IIRC the socket 939 Semprons use that core.
For an overclockable mATX board with PCI-E... "most" Geforce6100/6150 chipset boards allow a little overclock. One of the better overclockers is the Biostar Tforce6100 board (the blue board, not the red one). There were others such as the EPoX, but it is no longer available at the 'Egg. The DFI Infinity is also a good clocker, but I'm not so keen on the Southbridge chipset.