Journey Planner

By Car

AA route planner (for car journey planning)
Google maps (for public transport and car journey planning)
RAC route planner (for car journey planning)
Ordnance Survey (maps)
Red Planet Travel

By train

National Rail enquiries (for train journey planning)
TfL plan a journey (for public transport in London)

By Bus

TfL plan a journey (for public transport in London)

By Bike

Cyclestreets (for cycle journey planning)

On foot

Walkit.com (for walks)

General

Royal Mail (find a postcode or address)
Traveline (for public transport)
Traveline south east (for public transport)
GoEuro (for public transport)