http://www.learn-to-draw.com/ - my sons absolute fav learning to draw site
http://www.googleartproject.com/ (my absolute fav! You can view, most of the worlds most famouse works of art!)
http://www.historyforkids.org/crafts/ - this is one of the great sites I use for matching art to history!
http://www.abookintime.com/crafts/projectsmainworld.html - another great history crafts site!
http://familyfun.go.com/crafts/crafts-by-age/ - one of my fav craft sites!
http://kidswhothink.blogspot.com/ - this is my favorite rainy day art. This blog posts creative ideas, like building a robot out of your junk drawer. The kids than can post a pic of their creation to the blog!
http://www.dltk-kids.com/new10.htm - great craft ideas, especially for the younger crowd.
http://www.squiglysplayhouse.com/ArtsAndCrafts/index.html - one of my kids favorite art sites!
http://kidsart.com/blog/ (they also sell great kits)