Windows: If you're a fan of passive information delivery, AeroWeather is a clever weather tool that gives you subtle feedback about the weather conditions via Aero's colour scheme.
AeroWeather can change the colour of Aero based on the temperature outside as well as the atmospheric conditions. Cooler temperatures yield a darker purple theme and hotter temperatures yield a brighter red theme. You can set the scale to your own liking (if 10C is about as cold as it gets in your locale, for example, it's silly to leave the minimum at -10C). If you're using conditions instead of temperature, the interface changes to blue when it's sunny, grey when it's cloudy, dark grain when raining, and so on.
In addition to temperature and atmospheric conditions you can also set AeroWeather to monitor sunrise and sunset, brightening and dimming Aero accordingly. AeroWeather is freeware, Windows only, and requires .Net Framework 3.5 or above.