One easy solution is always HSTs, as you can arrange them in manymany different ways!
You might also want to check out patterns for charm packs, as you can easily cut a layer cake into 4 charms.
Have you checked Moda Bake Shop?
Here are patterns for layer cakes:
http://www.modabakeshop.com/search/label/Layer%20Cake
And here for charm packs:
http://www.modabakeshop.com/search/label/Charm%20Pack