Just in case leaving the tooth under your pillow isn't "official" enough, your child can fill out this letterpress certificate of deposit and leave his/her tooth in a silkscreened cloth deposit bag.
Here are the official "instructions" from Office of the Tooth Fairy:
Simply place tooth in the attached envelope and insert your completed certificate in the deposit bag. Place the full bag under your pillow. The tooth fairy will collect the Certificate of Record and place your compensation in the deposit bag.
A cute idea, a ovely keepsake, and pretty inspiration for DIY'ers. You can purchase one for $16.
Thanks to Oh Happy Day for spotting this one.