I race sailboats during the summer and I think I have a decent understanding of the weather.

http://www.weatherunderground.com
For the most comprehensive amount of info it can't be beat.

http://www.intellicast.com
Decent forecast, but there tempratures tend to be a couple of degrees high. The severe radar summary is awesome because it tells you how fast and in what direction storms are going. Also the windcast is awesome, it tries to predict at what time the winds will be at X Velocity and X Direction.

http://www.weather.com
The forecast tends to be the most accurate, but the radar kinda sux, and they make you pay if you want the most current data.

I forgot http://www.accuweather.com
As a company as a whole I think there great, and do a fantastic job forecasting, however there web site is miserable. If you see there forecasts on the TV, great, they do a great service with hurricane predictions. But there coverage of my home area is terrible, and there radar might as well be written in crayon.