Cross-posting this from STW since I think there will be plenty of interest on here:
http://www.natureonthemap.naturalenglan ... icMap.aspx

Loads of different datasets (including access, NCN routes, national trails, SSSIs, types of forestry, geology, common land, even sightings of rare species) that you can overlay on OS maps.

Fascinating (to me anyway) and potentially useful for anyone interested in the outdoors.