I like http://www.craftsnhobbies.com
it's not necessarily a child's craft site, but many of the projects are quick and simple. I really like how they are organized by holiday, special days, and seasons. We're doing a few Valentine's ones now.
I also really like the projects the kids do on the show Zoom. I don't get TV, but I check out their site periodically, and I have been doing their crafts, recipes, and science stuff with my son since he was 2. They are fun, and since I'm not so talented in this department, the stuff for kids is just right for me too!
Just go to http://www.pbs.org
and then click on the Zoom show's area.
Lastly, if you happen to be a Jan Brett fan (author of "The Hat," "The Mitten," "Hedgie's Surprise" and other absolutely wonderful children's books) you might go to her site:http://www.janbrett.com
We made the placemats and laminated them - very cool.
I also like Mary Englebreit's site - I'll look that one up again as I haven't been there in a while.