This is by no means a comprehensive list but a mere starting point. I cannot personally vouch for the credibility of lesser known marathons.
- Boston Marathon – http://www.baa.org/
- ING New York City Marathon – http://www.ingnycmarathon.org/
- Rock ‘n’ Roll USA Marathon – http://runrocknroll.competitor.com/usa
- Disney Princess Half Marathon – http://www.rundisney.com/princess-half-marathon/
- Tinker Bell Half Marathon – http://www.rundisney.com/tinker-bell-half-marathon/
- Thelma & Louise Half Marathon – http://www.moabhalfmarathon.com/tlhm/index.cfm
For marathons in your area, see Marathon Guide.com – http://www.marathonguide.com