This is pretty cool: Desktop Earth

Desktop Earth is a wallpaper generator. It will generate a high-resolution, accurate representation of the Earth. The imagery is based on NASA’s Blue Marble Next and Earth’s City Lights.

Day and night is accurately represented depending on the Sun’s overhead position (which depends on both the time of day and the day of the year) and both the snow cover and the foliage changes with the seasons.

Desktop Earth comes in two versions:

Online: You select the date and time, specify the resolution up to 1920×1200 (WUXGA), and click Generate. A high-resolution lossless PNG file will be displayed in your browser.

Downloadable: This is for Windows only. Desktop Earth will sit in your systray, run whenever you are logged on, and continuously update your wallpaper with an accurate representation of the Earth. There is no limit on the resolution, and the imagery is calculated from high-resolution 2560×1280 textures, so you can go wild with it even on 30″ flat panel displays. Multi-monitor configurations are also supported.

Notice how the ice expands and retreats in the northern hemisphere…