Simple, Lightweight London Travel & Transport App - easily accessible Travel For London Tools:
London Tube Map (works offline)
Live Tube Status / Train Updates (tube.lu)
Live Bus Status / Bus Schedules (TFL)
Live Tube / Train Departure Times (TFL)
Plan A Journey/Route(TFL)
Call For A Taxi (Call-A-Cab)
Pay Congestion Charge (TFL)
Top Up Oyster Card/Check Oyster Balance (TFL)

(TFL) services require internet access for up to date information and are provided directly by Transport For London