Visible Satellite Image: Essentially a "picture" of clouds taken from satellites in space. Visible satellite imagery is only available during the day since it relies on the reflection of sunlight in order to see cloud cover.
Infrared (IR) Satellite Image: Infrared satellite imagery is a measure of cloud top temperatures. With computer enhancement, the coldest cloud tops (corresponding to the tallest thunderstorms) are displayed as shades of orange and red. Warmer cloud tops (corresponding to lower clouds) are displayed as shades of gray. The big advantage with this type of satellite imagery is that it's available 24 hours a day, 7days a week. This is due to the fact that it relies on heat detection for its imagery rather than just taking a "picture" of the clouds.
Water Vapor Satellite Image: This type of satellite image is actually a display of invisible water vapor in the atmosphere, not clouds. This type of imagery helps to show where the atmosphere is dry or moist. It is also valuable in tracking features high up in the atmosphere, such as the jet stream and upper-air disturbances.