http://www.xcracer.com/UK-Mountain-Bike-Event-Diary-Planner.php looks pretty comprehensive, as does http://www.sleepmonsters.com/v2_calendar.php
Is there one site that lists everything ?
comprehensive but missing all the gravity events
https://www.rootsandrain.com/calendar/#!/
https://www.britishcycling.org.uk/events?search_type=upcomingevents&keywords=&resultsperpage=30&series_id=&fromdate=18%2F02%2F2014&todate=&zuv_bc_event_filter_id%5B%5D=7&series_only=0&online_entry_only=0&distance=&postcode=
Roots and rain is bloody brilliant. Learnt that my mate had been on average all season 2.4%slower than his mate all 13 season.
I'll put in a plug in for our site:
[url= http://www.meet4rides.com/
http://www.meet4rides.com/ ]http://www.meet4rides.com/
[/url]
Admittedly a primarily Southeast Asia focus, but starting to get more events from UK and Australia
[url= http://www.marathonmtb.com/ ]Marathon MTB[/url] is great, especially for overseas events.
Australia based, so that is the focus but has most european events covered. Not good for domestic events. XC racer is best there.