Per other answers you've received here, consider this:
If you post your home on the MLS you MUST sign an agreement with a MLS member real estate broker.
If someone sees the listing on MLS and an agent contacts you and you sell the home to the agent's client, you must pay a commission to your listing broker who then pays that agent.
You must offer a cooperating agent's commission on the MLS at the time you post the property on the MLS.
An Exclusive Agency listing means if you sell the property to YOUR customer you pay no commission. You must be careful in this respect, however. Ask each prospective customer if they are working with an agent and have them sign something that say's "No, I'm not working with an agent." Failure to do so could result in you paying a commission anyway since many buyers would say no when they were, in fact, contracted with an agent for representation.
And, finally, think about this. How hard would you work for someone if you weren't sure you were going to get paid if you worked hard and did a good job? An agent only gets paid if they close the sale on your home at the price you want when you want it. An Exclusive Agency Listing usually means the agent HOPES something good will happen and they will get paid, but they are most likely not going to spend money marketing your home or holding open houses or otherwise trying to get the job done. Your home will most likely sit on the MLS for a while, like until you get tired of waiting for something to happen and call your agent up and tell him to properly list the home, which is the strategy behind most EA listing agreements. They are usually not the best solution for the client, frankly.
Listing a house on the MLS requires a licensed broker who has paid dues to the MLS that services your local area. Typically when selling a house you offer a 6% commission which is split with any co-operating brokers (usally 3% to the listing agent, and 3% to the buyer's agent). However, you can take advantage of flat fee listing services that offer a non-conventional ways to list your house on both Realtor.com and your local MLS.
Usually these flat fee services require an upfront fee, and do not assist you in selling your property unlike a traditional broker. If you feel comfortable selling your house without the assistance of a licensed Realtor, using sites such as http://www.soldbymls.com or http://www.congressrealty.com can save you some money. However, if you are a first time home seller, or uncertain about how to properly sell your home I recommend using a licensed Realtor in your area. When using a local brokerage you typically get the services of a normal listing coupled with that broker's expertise in your market.
An Exclusive Agency Listing (EAL), as alluded to in previous comments, is the only way you can do it without paying a commission. But if the broker you list with finds a buyer at your price & terms stated in the listing agreement then you are bound to pay him/her a commission.
I do EAL's because I am a small realty-mapping company with a great deal of flexibility compared to franchise offices. All my listinhgs get full world exposure on Realtor.com Showcase. Contact me if you wish to do business.
P.L.S. Tony Novotny
Many franchise realties lack flexibility in this regard. I run my own company. I will do what is called an Exclusive Agency Listing, meaning you get it on the MLS - more importantly, on Realtor.com - and you pay no commission if you cause the buyer to come to you.
Tony Novotny, PLS-Broker
Only Realtors can post on the MLS. You might be able to find one that would list it on there for you for a flat fee but unless you know all the Real Estate laws (including all disclosures required), you might want to hire a Realtor to assist you - so you don't possibly face litigation in the future.