I found this artist's work to be inspiring. Interview with Daniil Alikova from The AREA http://xrl.us/DaniilAlikovAREA

Noticed I was using the same sky image in too many renderings and decided it was time for something new. I intend to do my own photos when I see the kind of clouds I want. But for today I searched for some to use right away. Ended up getting what I needed from cgtextures.com. MANY nice 360 degree panoramas. http://xrl.us/cgtextj