The following is the absolute best, you can get anywhere from here:
http://www.princetonol.com/groups/iad

Sanford Art Company: Interesting unit on architecture for younger students:
http://www.alifetimeofcolor.com

Excellent vocabulary and artists on file:
http://www.artcyclopedia.com/index2.shtml?9999

Not all links work-but worth a look:
http://www.artjunction.org

Intricate lesson plans, but worth a look:
http://www.getty.edu/art

Ditto:
http://artsedge.kennedy-center.org

Busy Teacher’s web site:
http://www.ceismc.gatech.edu/busyt/art.shtml

I haven’t explored this as much as I would like:
http://www.kn.pacbell.com/wired/art2

I learned about this from one of your very own Ocean Knoll K-2 teachers,(I apologize for forgetting her name.) Great site for artists:
http://cgfa.floridaimaging.com/

Straight from the Louvre and worth the visit:
http://www.ibiblio.org/wm/

Check out other students’ work + lesson plans galore:
http://www.artsonia.com/

Some interesting interaction work!
http://www.artsconnected.org/toolkit