I've used three, Accuweather, Yahoo! Weather, and Weather Bug. They are all usually pretty consistent. I like anything I can see a map and use the time lapse feature to see the storm coming in. Based on the predictions and the history of movement over the last hour, usually it is fairly easy to see roughly when it will storm. We've had a lot of rain in NC recently and I've used that to gauge doing yard work or just going out on my bike and such.
I rarely just take the forecast with anything more than a grain of salt unless I'm looking at hourly predictions. I think weather.com also does 15 minute intervals.