Unfortunately, right now there are many more people who want to get rid of their timeshares than those who want to buy them. There are many resale agents in this market. The most important thing is not to go with one who gets a flat pre-paid commission up front. These agents are successful because they tell owners that they can get a price for their timeshare that is higher than other agents. Then they take the commission and the property does not sell, because it is overpriced. They may not even actively try to make a sale.
As the market is not good for sellers, many owners opt to donate their timeshares to charity for the write-off. If this is not a good option for you, you could try auctioning it on e-bay. (they have a timeshare and real estate section) If you decide to go with an agent, there is a very good list of things to keep in mind when you choose one on this site: http://www.timesharetrap.com/sell_a_timeshare_with_reseller_agent.html
Another option would be to see if your property could be listed on the timeshare dump. This is a project that simply takes it off your hands by assuming the maintenance and other obligations, but will not pay you for your ownership. This route is for people who cannot afford to keep up their ownership and do not want to default. Their site is: http://timeshare.qcommerce.com/default.htm#tdump
If you decide to sell, be prepared to take a loss or wait a long time before you can get the price you want for your timeshare. Good Luck!