Multidays.com provides news in three main categories – multiday races, 24 hour races and international ultramarathons.
Ultrarunning World focuses on UK news and UK runners in races around the world and is also the home of Ultrarunning World magazine.
There are other sites that form what I have come to call the Ultra Running Network (URN) and these include the original domain Multiday Running.com which is a collection of multiday race reports. The original site was unfortunately lost.
There is also a smaller site, Stagerunning.com which has Stage Races as its focus.