I've been doing this about a month now and made an extra $200 or so from auctions with stuff I have gotten for free through
FreeCycle.
FreeCycle is a place where people post junk that they have and no longer want. If you want it, they will give it to you for free if you go and pick it up. So the only price you pay for anything is the gas to go and pick up the item.
While a lot of the stuff isn't worth too much, there are some things that people give away that they don't realize the true value of (or they just don't care). Get these items and you can turn a good profit rather quickly.
The competition on getting good items is getting much stronger as I'm sure I'm not the only one reselling. It has also been a great place to get weird and strange items sell on auction for free.