The following are links to some sites I have found to be interesting and informative. The list will vary from time-to-time as new sites are added and some migrate to other pages here.
One site deserving special mention is the Penn State University User Weather Observations Page. This site allows home weather observers around the world to post their weather observayions to the web where they can be shared and automatically plots these obs on national, regional, and state maps. Check it out!
The main list consists largely of sites devoted to severe weather.