While I was looking for the format of links to the OS GetAMap service for my last post I came across this useful list of online maps for the UK, which it seems has been lifted straight from Wikipedia - why they didn't just link to the Wikipedia page I have no idea. I particularly liked the content of the Magic website, which as Wikipedia says "is a web-based interactive map intended to bring together information on key environmental schemes and designations in one place", although the presentation is a bit clunky when compared to something as slick as Google maps, although Google in turn suffers from not being based on the OS mapping, so it's pretty useless outside of urban areas.
And by the way, if you do want to link to somewhere on the OS's GetAMap service, the format of the URL is
with the normal OS grid reference appended onto it, e.g. http://getamap.ordnancesurvey.co.uk/getamap/frames.htm?mapAction=gaz&gazName=g&gazString=TQ302795