I really like the mashup of data that has been done by a chap named Tom Taylor on the number of cycle accidents in 2007 and their exact location. To put together this map, the government released some data co-ordinates from the police about where the cycle accidents happened in London, Tom Taylor turned these co-ordinates into grid references, and those references were then able to be displayed on a Google map.
The Times website have a giant cycle accident map, which I've grabbed a screen shot from. Predictably, the accidents that occurred in the SE11 area mainly seem to have happened on the large main roads. Also, we seem to have far fewer accidents in South London than in the area immediately north of the river. Is that because there are fewer cyclists in South London, I wonder?