I really like Tomas and Axel Wennström's new weather site Vackert Väder. In Hollywood pitching lingo: "Vecka.nu meets SMHI".
Some of the things I find they do very well:
* Focus. It is all about the weather.
* Customization. Using geo-IP data to make an educated guess and customize the service for each user.
* Simplicity (the weather today on the first screen) combined with depth (the weather for more than 25,000 places for up to ten days)
Come to think about it, focus, customization, simplicity and depth are four character traits many good web sites share.