Helpful websites based on OpenStreetMap
Dhm
Shows a heatmap based on the distance a motorcar has to drive to reach the center of the map
Dist
Calulates distance between two points on earth and shows the shortest geodetic line between them
Gll
Allows to find a place on earth by name and shows latitude and longitude of it
Mobilemap
A Map display optimised for mobile devices with small screen and without javascript. Offers a variety of base maps and overlays.
Pgc
Allows to draw lines of constant geodetic distance ("circles") around points.
Vgr
Displays items of a GeoRSS-Feed as on overlay over OSM tiles.
Mapstyle Explorer
Interactive gallery of different map renderings based on OSM data.