Here are the places I go to get free or much discounted furniture for my nonprofit.

1. http://www.IReuse.com [1] Provides all free furniture and other items for nonprofits. I created a wish list on their site, and have been able to get the majority of the items on my wish list.

2. Industrial Surplus Foundation [2] Discounted Furniture and other items for Nonprofits. I filled out a small application and was able to purchase furniture at a huge discount for my organization, like desks for $20-$30 etc.

3. http://www.FreeCycle.org [3]  I just learned about them from a colleague. They have a series of e-mail lists where people post what free stuff they have and you can also search for items on their website.  

4. http://www.Craigslist.org [4] Lately I have seen a lot of great free stuff listed there.