There are dozens of strap-on fisheye lenses that you can buy nowadays for iPhones. Blame it on Lomography and Hipstamatic, perhaps. Pixeet's goes a step further though, letting you shoot full 360-degree panoramas with the camera lens and free app. »
Over at Instructables, user Banjomaster shows how to make a fisheye lens for his Nikon D90 for just $16, with the help of one of those wide-angle doorway peephole lenses.
Take a look at these trippy photos taken by Flickr user heiwa4126 using an ultra-wide fisheye lens. »