Have you heard of Freecycle? If not, you're going to hear about it now. I discovered it through blogger Sarah over at Going Jesus. Have something you need to get rid of but somebody could use? This is the place for you! It's organized through Yahoo Groups on a regional basis. For instance, I'm on the group for the county where I live. I imagine if you're in a huge metropolitan area it might be organized by parts of town, but I don't know. So far we've gotten rid of a huge pile of moving boxes (somebody's always looking for boxes) and picked up a nice full-sized sofa bed (score!) and a stack of oak-veneer panelling & mahogany window sills!
If you're penny pinching and willing to read the digest every day it's definitely worth your time.