Ordnance Survey Mapsat last the O.S. are providing some useful material on the net - try get-a-map and free outline maps, plus details of all the latest O.S. products.
Expedia Mapsall sorts of maps from all over the world
Multimapenter your postcode (or any postcode) and get a map...
Map Skills:
ScaleCentre for Topographic Information (Canada)- a simple explanation of how scales work on a map.
Map TermsCentre for Topographic Information (Canada)- a glossary of words used in mapping.
Map SymbolsCentre for Topographic Information (Canada)- useful examples but remember they are not all the same as those on UK maps
ContoursCentre for Topographic Information (Canada)- a simple explanation of what contours are.
Using a CompassCentre for Topographic Information (Canada)- starts off with a complicated explanation of 'why north isn't north' (!) but at the bottom of the page is a useful section on how to use a compass.