I've had this idea to find a way to connect landscapers and homeowners to people seeking to buy yard waste for use in various composts and mulches. What gave me this idea was that I had a tree cut down and chipped in my neighborhood. By simply asking, the guys gave me a huge pile of wood mulch! I gave them $50 as a tip. Had I gone through a mulching company, I would have paid closer to $300. I feel like there are lots of opportunities like this that exist.

Drawbacks: Very seasonal in temperate climates. Getting initial providers. Fluctuations in supply/demand. Some communities process yard waste for free.