You can try to FSBO in a hot market, it is worth a shot for a few weeks (less than a month, cut your losses early). If you do this, create a small brochure, offer a flat buyers agent fee, and then walk the brochure / leave copies at 10 closest realtor offices nearby, with the agents (and clients) showing date / open house.
See what happens. Many agents look for pre-sale / pre-listing information for their clients, and if your property is a good one, with a good price, then it could sell quickly.
Also, let your neighbors know, especially if you are in a condo, because sometimes they want to move up into a nicer property, or have a friend looking to get into your school district.
After 2-3 weeks of effort at this, switch to one of the low cost MLS listing services the others mention. I would only go for the agent if you need a lot of hand holding, or are trying for aggressive over market bids, in which case, select a realtor with a lot of experience doing just that. It takes a lot of experience to do it well, which you and many other full service agents don't have.