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Traveline South & East
Traveline South & East allows users to "plan journeys by public transport across the South & East regions of England (including Greater London) using Bus, Coach, Rail, Underground, DLR, Tram and Ferry services. The traveline south & east app also incorporates NextBuses for England, Scotland & Wales". 
Traveline South & East can navigate by post code, geo-location and point of interest. Journey plans can be saved to the iPhone to be checked when not able to connect to the internet, which is required to create a journey plan.
It uses public transport information for the South East, East Anglia and East Midlands Traveline regions as well as Greater London. It has nation wide train schedules.
There is real time bus tracking in areas where it is available, i.e. most of the East Midlands and the South East. 
Malcolm Barclay, an iPhone developer was behind Traveline South & East. He has developed London Bus, Tube & Rail Journey Planner among other transport related iPhone apps.
Traveline South & East was released on 04 May 2010.
mbarclay.net - Malcolm Barclay's blog.
Traveline South & East - iTunes apps store.