wunderground
good set of visualizations (temp, cloud cover, dew point, etc), can switch weather stations or have them average out the data, almanac, animated maps with specific overlays. This is my go-to prognosis site for most reliable forcasts, though weather is dynamic so I check it when needed and not as a prognosis in the morning is written in stone for the rest of the day.
earth
this is just awsome! real-time animated map-views by user specs.
These are good for common needs... my sailing weather tools are more in-depth.
windguru, it has a free version and another "premium". Good and accurate when you are away from town, and there are surfers or outdoor sports that require this data.
Intellicast is pretty good, with the historic data and forecast up to 10 days
well, this is my collection tools for checking how exciting my sailing is going to be (or not). A lot is over-kill for most people, but in case anyone has the need, here ya' go (sorry if i duplicated any from previous posts):