Hair

If you're getting a haircut, grab the extra hair and put it out on your lawn or in a bush.  It's organic so at worst it'll break down, and birds like to use it to make nests.

Another option, if you have a lot of hair or are a haircutter by trade is to send your trimmings to Matter of Trust where they use it to make mats for cleaning up oil spills.

Finally, if you are cutting hair that is longer than ten inches, you can send it off to Locks of Love. They weave them into wigs and give them to people who have lost their hair to cancer and other diseases. It's a great cause and a great re-use of your hair.

PROS: Helps others

CONS: It's a bit of a pain to collect the hair but it's not too big a deal.