Source: http://feeds.gawker.com/~r/lifehacker/full/~3/Bl04Vm-0nbs/create-a-faux-fisheye-effect-in-photoshop
For the unfamiliar, a fisheye lens is a lens with an extremely wide angle of view. For comparison, fisheye lenses have an angle of view of 180 degrees, but the fixed 50mm lens, a staple of basic photography, has only a 46-degree angle of view. Because of the huge angle of view, fisheye lens have a significant amount of distortion—normally a bad thing, but also an artistic result for some shots, and one of the reasons people use them in styled photos and videos.
Why recreate the effect in Photoshop instead of just using a fisheye lens? A fisheye lens for a DSLR from a no-name company will run you more than $300, and easily $700 and up from a respectable company. Unless you have a huge passion for fisheye photography or a pressing business need to take wide-angle, that kind of expenditure is outside the scope of most photography hobbyists.
Helen Bradley's tutorial on software fisheye effects requires just Photoshop, or the GIMP, and the patience to translate the steps to suit your photos. In most cases, you'll need multiple pictures of a single scene to replicate the wide angle of view you get with a fish eye lens. Using Photoshop, you stick the photos together, clean up the edges, and then use the distortion filters to bend the photo to your fisheye-loving will. For more details and a step by step walk through, check out the link below.