Here's a worldchanging small business: Seattle-based Urban Hardwoods harvests urban trees at the end of their lives and uses the wood to make fine furniture:

Urban Hardwoods reclaims urban trees and from them we make extraordinary furniture and architectural materials. Because urban trees are well cared for and are often given lots of room to grow, they develop beautiful grain character and are often larger than trees typically found in commercial forests and tree plantations. There is no better material in the world for making furniture than urban trees.

Thousands of urban trees come down in our city every year. Typically these trees are burned, chipped or taken to the landfill. Our mission is simple: to put this abundant and valuable material resource to its highest use by turning it into extraordinary furniture and architectural elements.

They're Smartwood certified and LEED-compatible, and obviously, moving urban trees from waste stream to valued resource is a good thing right up front. Their furniture rocks, too.
(Thanks, Jesse, for the tip!)