The following books (available at Amazon.com) are good sources of information on vultures.
Vulture: Nature's Ghastly Gourmet
by Wayne Grady
Vulture (Remarkable Animals Series)
Birding in the San Juan Islands
The Raptor Almanac: A Comprehensive Guide to Eagles, Hawks, Falcons, and Vultures
by Scott Weidensaul
Vultures (Wild Birds of Prey)
by Deborah Kops
I Wonder Why Vultures Are Bald: And Other Questions About Birds
by Amanda O'Neill
Living with Wildlife: How to Enjoy, Cope with, and Protect North America's Wild Creatures Around Your Home and Theirs
by Diana Landau, et al.
Going Wild in Washington and Oregon: A Guide to Northwest Wildlife Viewing
by Susan Ewing
Washington Nature Weekends
by Patricia Sunny Walter, Janet O'Mara
Watching Wildlife (Watchable Wildlife Series)
by Mark Damian Duda
Photographing Animals in the Wild: Photographic Hints and Tips
by Andy Rouse
for prints & posters of vultures and other birds.