Home theater specific motherboards are actually rather rare. The only company that consistently makes motherboards which are oriented towards the home theater market is Zotac, which has a very fine line of mini-ITX motherboards and tiny, barebones systems. But now MSI appears to be getting in on the act with the new MSI 740GM-P25. This Micro-ATX motherboard supports AM3 processors, has a PCIe Gen2 x17 slot, two DDR3 RAM slots and 6 SATA ports as well as Gigabit Ethernet and VIA 8-channel audio.
The new board should be arriving within the next week or two, and will ask that you part ways with only 59 of your hard earned dollars. That is a really good deal. I love the Zotac boards, but they do usually cost well over 100 bucks. Combining the MSI 740GM-p25 with a cheap Athlon dual core would result in a nice HTPC with a very low price tag.