I've just ordered one of those GiSTECH Phototrackr Minis, with the travel kit. Looks like it will do everything I need, and it's certainly not expensive.
My only question, which I will find out when I get it, is if it can handle the output of more than one camera (assuming that I don't have two photos taken at exactly the same time on two cameras). The device works by syncing the times in the EXIF data with the tracking points in its log, so I can't see that multiple cameras would be a problem, with the proviso mentioned.
And even if two photos WERE shot at the same time on two cameras (eg self and wife) then theoretically the system should still assign the GPS data according to the times - as long as we were both in the same place....
I'll let you know how well it works etc once I have it and have tried it out.