I've been thinking about this, too. My 7 and 8s are both making
sketchbooks (bound books with tissue paper collage covers that are turning
out really well!) and some of them are finishing much earlier than others.
I've decided to give out the first sketchbook assignment (post it on the
board as they come in) so that they can begin working on it when they are
done. I've taken assignments from the list that was posted here earlier
and also from the Elements and Principles of Design Posters and Teacher's
Manual from Sax. This has really good short assignments. The first one
that I am using (I think it was one of the ones from this list) is to draw
something distorted (ie pencil - short and fat, rather than long and
skinny). So, each week, I will post the sketchbook assignments and this
can be bell work for those who come early, and for them to do when I am
taking attendance, and also if they finish early. Also, I think the idea
of having stations is a good one. I have a pretty large room, and am
thinking about setting up one or a couple of stations at a time that they
can go too if they are finished. And finally, I have some art games
(puzzles of famous paintings, a card game from the Art Gallery of Ontario)
that they can play.
Hope this helps.