Here are some other sites to which we contribute weather data. Weatherforyou does a particularly nice job of integrating our data. You can also check out our generous host's home page at The Stewart Site

The Citizen Weather Observer Program is a really great, grass-roots effort to gather data from private weather stations, apply some Quality Assurance to it, and make it available to a number of research organizations.
Anything Weather is a relative newcomer to this area.

 

WxWatch is a site that is associated with Ambient, and only accepts data from users of Virtual Weather Station software (in addition to NWS data). Overall, they do a nice presentation.
Weather Underground is a direct descendant of the Blue Skies weather program (gopher client) available for the Mac a long, long time ago (early 90's).
Weather For You was about the first site to actively solicit data from private weather station users and make it available on the internet. It's basically run by one guy with a passion for weather, and he's very nice to work with.