sites and services that make use of OpenStreetMap
Turn your spreadsheet into a map
similar to Mapnik but with a different look (and unique layers)
create PDF maps with Street Indexes, grid finder, etc.
compare all sorts of map styles (this link directs straight to the Admin Boundaries map)
to browse through different floor plans and levels that are layered on top of each other
an OSM-based alternative to "Google My Maps"