Actually you can, of course, market and sell you home For Sale By Owner. The question of "Listing" it depends on where are talking about listing it. The Realtor MLS requires that it be listed with a Realtor. Some websites do not have that requirement. Also, if you are going to sell it yourself you really need to use an Attorney. The process is not as simple as it once was..
In my email today was a message from the KCM (Keeping Current Matters) blog that addressed For Sale By Owner considerations. Here is the link. Might give you some insight into the process. http://www.keepingcurrentmatters.com/blog/
Hope this helps. If you decide you need some assistance (or just some questions answered) from a Realtor - my husband and I have been around a long time and would be glad to talk with you