Sometimes being alert to what's on the street is enough. Even in my own, less-than-upscale neighborhood, I've picked up post-garage-sale finds ranging from clothing to file drawers to my very own Oakland A's baseball cap (I'm not a native, but I'm told it's a must-have around here.)
And the online world has added a new layer of possibilities. If you're not yet addicted, check out the free section of Craigslist. (It's there under "For Sale.") In the SF Bay Area, at least, you'll find everything from desks to dirt to dressers.
Another favorite is Freecycle, a grassroots nonprofit where members both advertise giveaways and post requests for what they need.
And for more tips and inspiration, see this September 5th USA TODAY article by Jayne O'Donnell, "If you can't afford it, then get it for free".