Many of the calendars list exactly the same races so it’s more about which one has the best and easiest search interface for the type of races you are looking for. I tried to cover those that I think are most complete and searchable but there surely are other calendars worth noting here, so just let me know in the comments and I’ll add them to the list.

Ultrarunning.com: Ultrarunning.com folks have just created a new great calendar for this 2010. The list of ultra races is long and they have build a great search interface: you can search by date, distance/time, state, terrain and even surface. Each race has a short description to get the basic stuff before clicking on the race website.

run100s.com: Stan Jensen maintains one of the oldest and best sources for ultrarunning races information, and the calendar is also a comprehensive one. You’ll find quick links for U.S. 100milers, for West Coast races and many other country-wide events. No search interface but just text listing with links to race websites.

realendurance.com: not just running, but endurance sports in general, this site has a visual map of races (mainly in the U.S. but also a few more from around the world). You can quickly check races classified by sport (running, triathlon, cycling), date and distance.

UltramarathonCalendar.com: A sort of “spin off” of ultrarunningnews.com, this site is exclusively dedicated to compiling ultra race info. You can click to sort according to various criteria but there’s no link to the race site, which will force you to do an extra search on google.

trailrunner.com: The American Trail Running Association has a great US race listing and a few international events too. Searchable by state or month, it has just the basic event info and a link to the website for further details.

trailrunnermag.com: Not much to say here. Simply the most comprehensive trail running calendar for US events. Searchable by state or date, it doesn’t have the best interface or a short description of each item, but you’ll surely find the race matching your needs. Their listing has also a printed edition that went out last month.

Ultramarathonrunning.com: This is a website dedicated to ultra racing which has a good number of events listed. Races are classified by continent and there are special categories for U.S., Canada, U.K. and Ireland. Short, extended info for each race listed.

multidays.com: Good source for international ultra and stage races. Events are split by distance and type (stage races, 100mile, 100K, 24hours), so if you are looking for a certain kind of race no matter the country where it’s held, this may be a good site for you. Basic info on each race listed.

Clubfatass.com: The Club Fat Ass runners had put together a list of ultramarathons for this 2010 happening in Canada. Short description, website link and contact info.

trailrunningsoul.com: And, of course, there’s a calendar right here on TRS. It’s not the most complete calendar (by far) but on top of North American events I also try to include events from around the world. The nice feature of this calendar is a visual interface which pinpoints each event on a google map and makes it quick and easy to find competitions spots at a glance.

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