Currently redirected to Nominatim
We used to have a page here at "Search" on how to use the OpenStreetMap.org front page search box (old defunct content now at Namefinder search doc)
Redirecting to Nominatim is probably a reasonably approximation of that these days. Trouble is there are other Search engines. In fact there's even other search matches appearing on the OSM front page.
-- Harry Wood 03:27, 25 January 2013 (UTC)