Today TfL have announced that contactless payments will launch on TfL services on the 16th September 2014.
However, don’t go throwing away your Oyster card just yet as it is what it says: TfL services only and not the current contactless travel on the buses, nor (officially) National Rail services in London (the contactless pilot has worked on National Rail).
However it appears that TfL hope to have National Rail services on board by the launch date and are working with Network Rail to enable this.
Diamond Geezer has an excellent FAQ about the contactless system on his blog.