For the most part, windsurfing wetsuits are just like any other type of wetsuit. They are almost always made from neoprene and are designed to be both flexible and to provide insulation against the chill of cold water. They are also available in many different styles.
When searching for windsurfing wetsuits, the thickness of the construction material is an important consideration. A thicker wetsuit provides a higher degree of insulation, and is therefore better suited for colder waters. Of course, if you ride in primarily warm water, then a thinner suit is a perfectly acceptable alternative.
Windsurfing wetsuits can be expensive, depending on the specifics of their design. However, with these suits you often get what you pay for, and as such it is recommended that you but the best that you can afford. A quality suit will often last for many, many years before it has to be replaced.