Heli News
International index of helicopter taxi and helicopter charter firms.
http://www.helinews.com/companies.html

Heliport Search
Index of stolports, heliports, balloonports, gliderports, ultra-light landing strips and seaplane bases all over the US.
http://www.rotor.com/fox/heli-2.htm

Just Helicopters.com
Features over 850 helicopter related links, including helicopter tour and charter companies.
http://www.justhelicopters.com/helicopter_links.htm#tour

Landings.com
A-Z of specialty air tour operators worldwide.
http://www.landings.com/_landings/pages/travel.html