1) Freecycle Freecycle is a yahoo group in which 10,000 boston residents e-mail about items they are giving away. Each e-mail comes with the neighborhood in which the item is located so pick-up can be easily arranged.
2) Craigslist This is the more obvious choice, but still, there are some great things on there. When people need to move, and have to get rid of their stuff fast, craigslist is the easiest way to do it! In fact, I just bought this huge mirror off craigslist for $10, and get this, I have to walk less than a quarter of a mile to get it!
Lets face it, craigslist may be the world's easiest way to REDUCE, REUSE, & RECYCLE!