Following are links that are useful to pilots as well as anyone working on their private pilot or other rating.

NOAA
NOAA provides daily weather forecasts, severe storm warnings and climate monitoring to pilots and other professionals.

DUATS
DUATS is a Free FAA Sponsored weather and flight planning service for pilots.

Lockheed Martin
Provides users of the National Airspace System with pre-flight, in-flight weather briefings as well as a host of other services.