The calendar format for RiderHQ is quite nice and being able to download the ics file (although it doesn't appear to be correctly generated!), shame you can't filter my region or category.
I thought the BC one was quite good for finding events in the right region with the right category:
http://www.britishcycling.org.uk/web/si ... future.asp(not that I've entered anything... yet!
)
--edit--
The trouble with that active one is it doesn't appear to be focused on any particular sport or region, say for example I'm interested in events in the south of england, the only filtering is either by country (too wide) or shire (too narrow).