If you're in the market for a smaller-than-usual motherboard, chances are you'll end up with a Mini-ITX board, as it is increasingly growing in popularity. VIA has several different boards based on this form-factor, and have just recently released a new one.
The VIA EPIA LT features dual-LAN and dual LVDS and comes with either a 1.5GHz or 1.0GHz processor. If you're looking for a silent configuration, you'll want to go with the 1.0GHz model. It has a variety of I/O ports including four (yes four) COM ports, a PCI slot and 6 USB ports.
The board supports up to 1GB of DDR2 and has VIA's UniChrome Pro II integrated graphics processor. The IGP can do 2D/3D graphics as well as MPEG-2 encoding. The EPIA LT is geared more toward POS and digital signage systems than regular PC applications, but I'm sure you'll be able to find plenty of uses for it.
[via product page]