Features:

Covers every station on the London Underground's network.
Provides information for every exit and interchange.
The app also offers a guidance as to:
which way to continue once you're off the train. (Left/Right/Straight - where applicable).
on which side the doors open
how many carriages are there on the line you're travelling on.
Interchanges are colour-coded for easier identification (in line with current Tube line colours).
Can be accessed while you're on the Underground, or above the ground. In fact the app can be used anywhere. No internet or GPS connection needed as the App contains the complete database of the network.
Extensive information about the location of tourist attractions and the Olympic venues (in London). Great for domestic or foreign visitors!
Works on just about any Android device. The app has been designed so that it fits every screen size. iOS version is coming shortly!! (work is already in progress - expect to debut around mid-late June).
Costs less than a bottle of water. And imagine all the time it will save you!
DLR and Overground info to be added soon.

Screenshots: