Use these museum and gallery links to access works of art.

http://www.nga.gov/kids/kids.htm
http://www.guggenheim.org/
http://www.metmuseum.org/
http://www.paris.org/Musees/Louvre/
http://www.tate.org.uk/kids/
http://www.nationalgallery.org.uk/
http://www.britishmuseum.org/
http://www.vam.ac.uk/ - Victoria and Albert Museum
http://moma.org/
http://www.saatchi-gallery.co.uk/
http://www.balticmill.com/
http://www.getty.edu/museum/
http://www.24hourmuseum.org.uk/
http://www.mla.gov.uk/website/home
http://icom.museum/vlmp/galleries.html

Also, see the following page on the NSEAD main site:
NSEAD links

Lots of very good tips for teachers on this American website:
http://www.artjunction.org/