Geocache finds 'heat-map' generator
www.ozpoi.com - lots of useful Australian POI files
www.tomtompoi.net - various POIs including UK low bridges.
www.maft.co.uk/garmin/ - Garmin POIs
www.poidownload.co.uk - UK POIs
www.pocketgpsworld.com - Lots of UK POIs
Google Maps
Other sites
Feel free to suggest a site.