I'm currently travelling the world so these ideas aren't immediately useful to me, however I shall be returning to lovely old London in the future where some of these ideas would be great. My Mrs is a dev and I've given her a poke to have a look into them, but at this time they're not exactly a priority.
Using the APIs available from http://www.tfl.gov.uk/businessandpartners/syndication/default.aspx one could make some seriously neat instant access tools.
Ideas:
Journey Planner.
Access a list of stops on your watch (with favourites and/or recent lists) to say where you want to go. Use GPS to know where you are and the Journey Planner API to grab directions, which are shown on the watch.
Live bus arrivals.
Use GPS to to grab info using the Live bus and river arrivals API and show what buses are coming and going.
Tube information.
Access the tube departure board, line status and station status information. Display the local station info (GPS) or any other station from a list on the watch. This could be linked into the Journey planner jobby further up.
Boris Bike availability.
Use GPS and the Barclays Hire XML feed to display nearest available Boris bikes and where to drop off.
These apps would be really handy when getting around London. It's pretty neat of TfL to provide these tools and I think we should make use of them.
As mentioned, I'll try to get the Mrs to have a look, but I doubt anything would be forthcoming in the near future!