Just noticed the Windows Live Local (http://local.live.com/) now has street level mapping for the UK - something which wasn't present in the initial releases.
It also has a very rich UI and support for things like adding pushpins with a right click, a scratchpad, and mouse wheel support for zooming. In fact the UI is some way ahead of that offered by Google maps (maps.google.co.uk) IMHO.
If you want to use map services like these on your commercial site though, the choice between Google Maps and Local Live comes down to business models. Where-as Google Maps will eventually place ads on your maps, (see http://www.google.com/apis/maps/terms.html), Local Live will, I believe used transaction based fees and no ads.
HTH
Ian
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