I recently met Nancy, a photographer friend, at a meeting where we began talking about different aspects of photography, including the use of fisheye lenses. When I told her I had straightened such a photo, she asked how and I told her I would post the answer on my blog. The (almost) finished image is above.
I may crop it before printing so it looks something like this.
This is my original. I took it with a ProOptic 8mm Fish-Eye CS lens mounted on a Nikon D200 modified for infrared light. The lens costs $280 at Adorama.com and I enjoy using it.
To straighten the lines I simply added a guide line and then applied a series of warp adjustments (Edit/Transform/Warp) to a duplicate layer. You can limit the area of the image impacted by the warp by making a selection first. I then removed lens flair, did some burning and dodging, and added some structure and a little color to get my final image.
Using warp adjustments can be a little tedious, but the results are usually worth the effort. I always enjoy it when another photographer looks at one of my images and is not sure how it was done.