UK Ordnance Survey Topographical Map - with location, geopositioning, tracks, weather and Wikipedia
Mapbox Leaflet World Map - with location, geopositioning, tracks, weather and Wikipedia
French IGN Topographical Map - with location, geopositioning, GPS and Wikipedia
OSM OpenCycleMap - OpenStreetMap Cycle/Topo Layer
OSM Mapnik - OpenStreetMap Mapnik Layer
European Transport Map - map with rail, road and suburban links
German Topographical Map - physical and land use map
Google Map - layered on an OpenStreetMap background
Bing Map - with a Mapnik OpenStreetMap background
US USGS Topographical Map - hiking map with layers
Kompass European Topographical Map covering most of Central Europe
Ordnance Survey UK Historic Map - six inch series published between 1888 and 1913
Ordnance Survey UK 7th Series - one inch series published in 1947
Ordnance Survey 1:25000 Series - published from 1937-61
Google iPad Mobile Map - optimised for use with mobile devices
Google US Topographical Map - with US USGS topographical layer and Streetview
Bing Layered Map - Bing/London Street Map/UK OS 1:25000/Satellite/Bird's Eye
Here Functional Map - with routing, measurement and local search
Systematic Navigation - Excel-based solution for astro and onshore navigation