I want to avoid this site being a just a list of links so this is just a short (and subjective) list of sites that I like:

LetsRun.Com - The best site out there that I could find about what is happening on the international and national level in the sportLocal Sports Activities, Inc. - A pretty cool search engine for finding running, swimming and tri events throughout the US.
Kick Running Site A Site with a little of everything including training advice, races, etc.
Peak Performance - This is a great newsletter that has some interesting articles. Much better than the usual fluff that you get in running magazines, this focuses on professional fitness research  
Do It Running- This was once a great site. Now it is just average but decent for current track and road race news and trainig tips.
Runner's World Online - For a commerical site, they are pretty good.
Running Home Page
GBTC Running Resources Page (probably the most complete list on the Net)
Yahoo Running Page
Dead Runner Society
Running, Walking, and Fitness Publications
Fast Track Online A couple of things for the serious runner/ race director, but also a free running-related e-mail greeting card service that I thought was pretty cool
RacePacket Calendar and results for VA, DC, MD and DE
ActiveUSA.com A site that covers many sports and events and includes a VERY Complete race schedule for all states. This link is to the running events only.