Here in the UK we have an odd situation when it comes to mapping and government derived data. As far as I understand it, local authorities collect address point data, but Royal Mail holds the postcode data, whilst the Ordnance Survey have the very nice detailed map of the whole of the UK.
Unfortunately the licensing restrictions on OS data means that they would claim my work if I used an OS map as a base (something called a derived work I think). It all sounds very complicated and means that publicly collected and held data cannot be placed on Google Maps or Google Earth as this would contravene the OS license. I don’t pretend to understand it all but what it means is that purchasing mapping for planning applications or other purposes can be an expensive and confusing business.
Some people have pointed out that since the OS and Royal Mail are essentially government owned businesses that we the public should be able to use freely the data they have collected. This blog follows that campaign: http://www.freeourdata.org.uk/blog/
Want to help free the postcode as well try this site: http://www.freethepostcode.org/
OpenStreetMap is a start but some people would like more than roads! http://www.openstreetmap.org/
How about looking at out of copyright maps of the UK? http://www.npemap.org.uk/