Fun stuff on the Transport for London site.
An interactive clickable tube map.
Click on a station and you get a list of nearby restaurants and venues. Click on a venue and you get a streetmap that shows you how to get there.
Lots of fun but needs more content to actually become useful.
Shows you the same information as you see on the platform indicators.
At the moment it’s only a demo so only works on part of the Bakerloo line.
I suppose if you can get from your house to a London Underground platform in 3 minutes it might actually be useful too.