Wide angle lenses should be an essential part of the kit for any photographer. They are more versatile than you might think. Here are some ideas for uses of a wide angle lens:
Landscapes - Perhaps a more traditional use of a wide angle lens is to capture sweeping vistas of the natural landscape. The wide angle allows you to give a feeling of expansiveness and wide open nature to your shots. The effect can work especially well when you set up on a hill, looking down on an expansive landscape. Make sure you use a small aperture to get everything in the image crops, back to front.
Restricted shooting position - A wide angle lens is also ideal when your shooting position is restricted, such as when you can't move backwards or when working in cramped environments.
Streetscapes - Wide angle lenses are ideal for streetscape photography too. They can be used to create unique, distorted perspectives from street level looking up at skyscrapers, and fantastic vistas of the skyline at night fitting an array of buildings in.
Interior spaces - A wide angle lens is really good for shooting interior spaces as it gives the illusion of the room being more open than it actually is. Plus, a wide angle will allow you to photograph virtually all of the room in just the one shot.
Different perspectives - Wide angle lenses are great for photographing something normal from a different perspective and making it look unusual. For example, Shooting a portrait with a wide angle lenses can distort the person's features, with amusing results. The same can be done with animals.
Candid street photography - A wide angle lens is a great way to capture candids on the street as you'll still be able to capture the person or people of interest without having to focus your lens directly on them. It also means you'll be able to capture more when 'shooting from the hip', increasing your chances of capturing an interesting street candid.