Coffee grounds. There is a little place called Bella Latte I pass everyday so I stopped one morning and ask if I could leave a bucket. They were glad to oblige and now I get two 5 gallon buckets of them per week. They make each cup to order so they look like little coffee biscuits.
Its amazing how much free material one can accumulate with Craigslist, Freecycle, and just asking nicely works to.
