There are a lot of things you can sell on Ebay for no monetary investment--just a little bit of your time and energy.
SERVICES: There is a section in ebay titled "Specialty Services." Browse through it to come up with ideas. Do you have skills that may be in demand? Do you do copywriting, edititing, proofreading? Perhaps you have great design or HTML skills. What do you (or have you in the past) gotten paid for and how could you incorporate that into something to sell? Perhaps you are a whiz with accounting or taxes, you could list your services for online sellers or small businesses. Every one has skills that are unique or worth paying for. Get creative here!
TICKETS: Look at Ebay's section of tickets. Hundreds of tickets sell above face value every day on Ebay. You can buy tickets for a hot show or sporting event, it can be in any city, and resell them as the event gets closer. Watch what similar tickets end up going for and buy carefully. There is a lot of money to be made in ticket sales but make sure to study the market.
OTHER PEOPLE'S STUFF: You can quite easily become a trading assistant officially through ebay and be listed to do consignment sales. You can also solicit consignment sales on your own. After approaching friends and relatives, get creative. Call people who have items listed in the classified or on Craig's list. Many of these sellers want to unload their stuff but don't have the patience or inclination to sell on ebay. Consider approaching small businesses in your area. Offer to list slower moving items and split the profit. There are hundreds of small shops in every metropolitian area, you might be able to get a nice source on unique inventory.
Keep your eyes open and your pocketbook closed when first selling on ebay. There is a lot of potential profit out there at NO COST to you!