I've been tagging mostly residential roads, paths and cycleways, but want to start adding other features. The amenity-tag seems especially tempting.

amenity=pub
amenity=school
amenity=college
amenity=library
amenity=bus_station (and highway=bus_stop)
amenity=taxi
amenity=bank (and with atm=yes)
amenity=cinema (or amenity=theatre)
amenity=fire_station
amenity=grave_yard
amenity=place_of_worship
amenity=police
amenity=post_office (and amenity=post_box)
amenity=recycling
amenity=townhall

Besides those:

sport=golf (and others)
tourism=camp_site (and others)
leisure=stadium (and others)