This page has links to useful resources regarding environment spheres. There are many great panoramic images out on the net, some pay, many free, but they are hard to find. If you discover a great resource, particularly free stuff, and I don't have it listed, let me know.
NOTE: I'm pointing you to these resources (particularly the images) so you can experiment with them. But before you use any of these in a project, especially a commercial one, check with the owner regarding your right (or lack thereof) to use their images in your work.
An awesome resource - the first place you should go. Philo (Phillippe Hurbain) is a technologist who has made a hobby of taking and sharing panoramic photos
. This site provides dozens of free panoramic images, as well as lots of info on how to make these, and great links to other resources. I'm not going to copy his resources - go check his out. Particularly important here is his collection of panoramic sky photos
. These are a must-have. Get the "Equirectangular" images to use them with my environment sphere.
A few HDR outdoor panoramas.
"You can get decent photos out of a standard, consumer-grade digital camera, but a little post-processing can turn them into fantastic wide-angle landscapes. You don't need to be one of those people who can explain the concept of lateral chromatic aberration to get truly eye-catching digital pictures. With a few shutter clicks and some free, cross-platform software, you can easily mesh standard digi-cam shots into true landscapes, fix one photo's deficiencies with another, and create layered photo collages."