I read a number of blogs and web sites, as well as using email groups and forums. These are the ones I check regularly and find most useful.

1 Communities

Dailymile A great community of runners and other endurance athletes
Fitocracy More variety of sports represented than Dailymile, and just as good a community spirit

2 Blogs

http://mohammednc.blogspot.com Mohammed ‘The Sultan’ lives a life of adventure, and I join him vicariously
http://obsruntheoden.blogspot.com A great perspective on the Charlotte running scene
http://annettebednosky.blogspot.com – It is always worth following what good runners are doing
http://barefootted.com/ - Barefoot Ted, of Born to Run fame
http://dirtyjokesandstories.blogspot.com A little running humor, all ‘100% Factual’
http://www.irunfar.com/ In the past this has been focused on races, but recently changed to include gear reviews.
http://www.trainingbible.com/joesblog/blog.html some scientific based blog entries

Mangum Track Club. http://groups.google.com/group/mangumtc A group that puts on a number of ultras in the NC area.
Barefoot running. http://groups.google.com/group/huaraches/topics This group was started by Barefoot Ted.
VHTRC Virginia Happy Trails Running Club. http://groups.yahoo.com/group/vhtrc/messages?o=1 Good group for the VA based races.
University City Road Runners. This is a Listserv/majordomo style email list, but without the automation. If you want to join, come to one of the group runs and ask to be added. http://ucrun.com has the running locations.

Runners World Ultramarathon Forum. http://www.runnersworld.com/community/forums/training/ultra-marathons Very active with some very experienced people taking part
Runners World Marathon Forum. http://www.runnersworld.com/community/forums/runner-communities/marathoners Lot of activity - sometimes too much to keep up with

http://pponline.co.uk – the popups are annoying, but it's worth it for their analysis of sports science.