OS Map mashup

Of course it's far from official, but any halfway-proficient Google Maps API developer can plug OS imagery into the GMaps UI with a modicum of work. That's the irony in all of this - Ordnance Survey hasn't stopped their maps from being used in ways they don't approve of.

Postcodes are a similar story; Royal Mail owns your postcode, and you can't use it except at their pleasure. They have recently stopped Google from supplying postcode lookup through their geocoding API.