Here are a couple of available ones:
A wireless hotspot finder, by Kensington.
For Seattlelites, a pocket traffic monitor.
Here is a gadget that doesn't exist yet but I wish would: a pocket laser projection display. This is something I am sure we'll see more of in the years to come, because cellphone displays are really too small.
Stefan Marti, from MIT Media Lab, got a working prototype of a one line character display, called TinyProjector.
Symbol appears to be working on a full VGA display, that is not yet available.
Update: The NYT has an article on laser-powered pocket projectors.