I know this has been on the forum before but I just thought I would plug it again. For anyone who might need some free good quality hdr's this is a great resource. The book on the website The Hdri Handbook is also really great value for anyone in our line of work (especially if you just bought a new 550d and are just learning how to use it, like me
http://www.hdrlabs.com/sibl/how_it_works.html

http://www.hdrlabs.com/sibl/how_it_works.html