After re-discovering the cool http://wince.dentro.info/koord/osm/KosmosMap.htm by StefanDausR, I created a style for the Merkaartor OSM editor:
http://wiki.openstreetmap.org/index.php/Image:Merkaartor_Maxspeed_Style.png

If you don't run Merkaartor SVN, you can get the style from
http://trac.openstreetmap.org/browser/applications/editors/merkaartor/Styles/Maxspeed.mas and load it manually (Tools > Preferences | Style | (*) Custom).