The only US weather data that is available free for commercial use is the US National Weather Service. I'd like to use it. Is there a Ruby/Rails library for accessing it?
Perl would also be helpful. They provide a Perl example. I'd use it as a guide for writing the Ruby version.
The NWS provides a RESTful web service in addition to the SOAP service, but if your needs are simple, consider the outoftime-noaa gem on github. It provides a straightforward interface for obtaining forecast and current conditions data.
(Be warned that one of its dependencies is not yet compatible with Ruby 1.9.)