If you are a member of your local netmums site they do a buy and sell. U can also find out about nearly new sales in your area and you get part of the money and so do nct. If not why not do a car boot sale?
Local classified ads are usually a good way of selling stuff thats too big to post. You have to be prepared to be in for when people come around to look at the stuff though, which can be a pain.