Property (Estate Agent) Advertisement Websites

RightMove
HomesAndProperty
ZoomF
FindAProperty
HotProperty
London Guide Residential
PrimeLocation
PropertyFinder
PropertyMatters
RightMove
PropertyBroker
Homes & Property
ThinkProperty
London Property Watch

The Rat and Mouse - Property News in London

Also this brilliant website that has info on every property in the UK (used for house price index):
MousePrice