OpenStreetMap
Found the oscompare.raggedred.net site useful in flagging errors in my area but does not get it 100% right so had to survey while on a farm visit in the area, but is still a very useful tool.
Cleared quite a few errors in Hoo St Werburg area but still quite a few to do
Discussion
Comment from chillly on 6 November 2010 at 12:33
I used the very useful ITO tiles layer to create the site in the hope that it would show areas that need surveying, and not to just use the OS Locator names to replace OSM.
Comment from Vclaw on 8 November 2010 at 17:12
Yes, I've noticed quite a few errors in the OS Locator names - mostly minor misspellings, different spacing/apostrophes or old names etc. So best to survey on the ground, and check what the streetsigns say.
Though the oscompare is still very useful for finding areas that are incomplete, or need surveying. There's also Musical Chairs, which is a similar tool for comparing with OS Locator: http://ris.dev.openstreetmap.org/oslmusicalchairs/map