Here are some useful sites for weather information.
Convective Addiction – A group of storm chasers I collaborate with, detailed forecasts, case studies, radar analysis, great DVDs and more can be found here.
GR Level 3 – The most commonly used radar software among storm chasers and weather lovers. Easy to use and customize!
National Weather Service – The official source.
The Weather Prediction – Great educational site that explains things in easy to understand terms.
Twister Data – A very easy to use site for model data, great for beginners.
WeatherShack.com – WeatherShack.com is a leading weather station, wireless weather station and home weather stations provider, in addition to other weather instruments.