Google's official Nexus One Dock looks to be imminent, going by an advert spotted running on a YouTube video recently. The ad suggests that the dock will be priced at $45 and support charging the Nexus One, playing photo sideshows "& more".
The assumption is that placing the Nexus One into the dock will automatically kick off some sort of desktop display mode, similar to how the Motorola DROID enters a desk-clock and infostation mode when docked into its cradle. As to the "& more", that presumably refers to the integrated Bluetooth connectivity tipped by the FCC filing.
We've just checked google.com/phone and there's still no sign of any official accessories there.