Yeah, me too. I have had lots of good luck with both buying and selling on craigslist. Haven't heard of it? Well it's a free community where you can post what you have to sell, what you're looking for to buy (or sometimes be given for free), and where you can advertise your garage sale. It's the first (and usually only) place I check to see where the garage sales are happening, and checking craigslist before I head out has yielded in some great finds! I've also purchased some things on craigslist such as a futon and mattress (sold separately by two different buyers). The futon was black when I bought it, but after a few cans of white spray paint, it looks much better. It also came with a brand new black futon cover, still in the package, however since I don't like black furnishings, I bought a white one for it instead. I had to buy that new. *Sigh*
I also have had some good luck selling items on craigslist. Recently, we sold a TV and some wedding items, including a cake stand, lantern centerpieces, glass jars for a candy buffet, favors, bouquets, etc. You should totally check it out. Posting is completely free! And what is good about the whole thing is it's very eco-friendly. You're helping to keep unwanted items out of landfills by buying second hand.
Topic for another day.... freecycle.org :) Similar to craigslist except everything given away on freecycle is 100% completely free!