This wiki is no longer maintained as of April 2012. Existing users may update articles, however user registration is disabled.
WikiSPEEDia is a crowd-sourced database of geocoded speed limit signs.
The database has been growing over the year, as has demand for a speed limits database due to the proliferation of mobile apps to rely upon it. It's wikipedia page is being misappropriated as a place to list the apps that use its data. 
The database asks for a donation from commercial works, though remains free to use. 
Set up in 2005 as a data store for cruise control for cars to pull speed limit data from.
In 2009 a computer game was developed by school children in which they could "drive around" on Google Street View and record the speed limit signs they came across.
WikiSPEEDia - wikipedia article