just a few other additions:
- I warmly recommend FishEye Hemi for straightening out images. It is far better than anythng else I have tried.
- Unless you want a very strong fish-eye effect, keep the horizon and key vertical close to or in the center. It's hard to straighten out images that have the verticals or horizontals 2/3 to one side.
- Most fish-eyes do not accept screw-in filters. Either get a Cokin-mount or be very very careful..lol.
- Don't be afraid to get the sun in the picture - most fish-eyes do really well and have very little flaring
- Don't forget basic compositional thumb-rules in the excitement of using a fish-eye. They still apply - perhaps most of all: foreground interest.
Last, but not least: share some of them with us here?
Good luck - Cheers