My kids LOVE clank cans! Take an empty formula can (or something like it) with a slit cut in the lid. Use frozen juice can lids and mount a picture on the lids. Children put them in the can one at a time and get rewarded when it "clanks". You can see pictures of the cans at http://ccvillage.net/jycalv/albums/12/935.

For a couple of great patterns, go to:
http://www.makinglearningfun.com/themepages/ChickaChickaClankCan.htm

Your kids are sure to love them!

for another view of a clank can, go to www.ccvillage.net/nurturingnest/albums/111/782