http://www.techradar.com/news/photography-video-capture/cameras/best-wide-angle-lens-1307770

Next to a telephoto zoom lens, a super-wide-angle optic is one of the most popular accessories for a DSLR. 

Most kit lenses offer a widest focal length of 28mm equivalent, or sometimes even 24mm at their wide end. This does give your camera a pretty wide angle of view, but sometimes that's not quite enough.