UK Ordnance Survey Topographical Map - with location service, geopositioning, GPX track import and export, exterior GPS capability, local weather and Wikipedia entries
Mapbox Mobile Map - with location service, geopositioning, GPX track import and export, exterior GPS capability, local weather and Wikipedia entries
French IGN Topographical Map - Institut Géographique National map with location service, geopositioning, GPS and Wikipedia entries
OSM OpenCycleMap - OpenStreetMap Cycle/Topo Layer
OSM Mapnik - OpenStreetMap Mapnik Layer
European Transport Map - ÖPNVKarte with rail, road and suburban links
German Topo Map - physical and land use map
CyclOSM - OSM Cycling Map
Bing Map - standard street map
US Stamen Map - topo and hiking map
European Topographical Map covering most of Central Europe
Ordnance Survey UK Historic Map - six inch series published between 1888 and 1913 with modern overlay on a scroll bar
Ordnance Survey UK 7th Series - one inch series published in 1947
Ordnance Survey 1:25000 Series - published from 1937-61
Google Mobile Map - optimised for use with mobile devices
Google US Terrain Map - topo map with Streetview
Bing Layers - Bing/UK Ordnance Survey OS 1:25000/Satellite/Bird's Eye
Here Map - with routing popup, measurement tool and local weather