Fisheye lenses may seem like a cool way to experiment with your photography, but a fisheye lens doesn't have to be “all fun and games.” They are a wonderful opportunity to showcase your artistic side and they're more versatile than you think. The first order of business is to not confuse them with a wide-angle lens, although they do in fact capture a wide angle. The center of the image will appear somewhat normal while the outer portion is visibly distorted. A wide-angle lens has corrective elements to “fix” the distortion, unlike the fisheye lens.
There are two types of fisheye lenses: diagonal and circular. Diagonal is the preferred choice and will map a 180 degree angle view diagonally across the frame's sensor and fill the frame. A circular lens has a shorter focal length and creates a circular image centered in the frame. While these lenses might be awesome at funky pictures, you can utilize them in many situations. Because they're wide-angle, try them for landscape and nature photography. They also work well on architecture, especially on ceilings. Try moving in close to the subject for more detail, and if you use a shorter focal length, there will be less distortion.