Ebay is good, but I have found that many items for sale up there can go for more than the origional price.
Boy Scouts and Girl Scouts in my area have a 'sale' of used equipment on occation. They sell the old stuff to get new stuff and to go to campouts.
The University Surplus sells all sorts of stuff, and when I can get over there, I find everything from Lab equipment to furnature. The school systems also surplus out things on occation.
And, my favorite, Garage/Yard sales. You get to talk to the people who had it last, and because I am really going to use it, sometimes I get a discount after talking to the people. It is fall, many people have to clear out their garages to make way for the cars that are supposed to be in there.
Rena