Choosing lenses for your camera isn't easy, though. You want to get the right focal length for your needs. The focal length determines whether you get a wide-angle shot, a telephoto one or something in between. Wouldn't it be great if you could compare different focal lengths?
Both Canon and Nikon have lens simulators on their sites. Just specify the camera you're using and the lens information. You can see exactly what your images will look like.