I see you already have several answers, and I'll admit I haven't thoroughly read them, but I did notice the comments about the problems with the flat-fee MLS systems. I've listed and sold several properties that had originally been listed this way. We all understand how difficult the market is right now, and are sympathetic to the fact that so many people are losing the homes and equity. But I would encourage you to not waste your money by paying an up-front fee, when there's a good chance that you'll eventually have to go the traditional route of listing and paying a commission when the property sells.
Also, the MLS is not going to bring you even half the results you need, in order to get your home sold. It's still very powerful, but we're now in Web 2.0 which basically means the internet as 95% of the population knows it, has undergone a drastic change; it is now the most powerful means of marketing your home, when it is done right. But this means that you, or your agent would have been very quickly educating yourself to the web changes.
To effectively market any real estate, the property for sale needs to be on multiple web sites and blogs, all of which have the ability to be found by the average consumer who is doing a targeted search (through their preferred search engine) for the area and type of real estate they want. And once the property has been found in a search, through a major search engine, it needs to have plenty of quality photos, a description that quickly grabs the attention of the reader, and video if at all possible.
Last but not least, make sure you choose a REALTOR who has plenty of experience in this market, and who you feel confident has thoroughly familiarized themselves and their brokerage with your home. You can also request that they e-mail you a link to each site and blog where the home is being marketed. This gives you a way to track the progress as well.
Whatever avenue you choose, good luck!