A bit of Andy Goldsworthy on the web
Artcylopedia, with links to his work in museums & galleries (where I found a few of the other links on this page)
Center for Global Environmental Education
ArtsEdNet
UK Government Art Collection
Cornell University - Fall Creek Project
2k journal
Brief Smithsonian Magazine piece
Sweetbriar College
art in context
StudioInsite.com
Oh, and for Stephen...
NPR piece on James Turrell and his Roden Crater project.