Portwell also has an Atom board in the 3.5" form factor.
http://www.portwell.com/products/det...CHAR1=PEB-2736
I don't much like either board right now. iBase went with a PCI-104 connector instead of mini-PCI or mini-PCIe, and Portwell went with SDIO which is even less useful to me. At least I can find a PCI104 mini-PCI board.
Still hoping there'll be a good Atom board. Been playing with Geode GX1 and Via C3 3.5" boards over the last few days. The Geode@300Mhz pulls 6 watts of power and the Via@667MHz is about 15 watts. The Atom would be about half the Geode with 4-5x better performance. Just plain wow.