There's a reason that so many of the new online auction sites that crop up every day do not last, and it has very little to do with them being able to attract enough sellers. The real secret is that many of these web sites are unable to attract enough real buyers. Beyond the major venues that most sellers are familiar with, the real exceptions to the rule have often been the 'niche' web sites.
Web sites that specialize in selling in specific categories are a good way to expand the number of channels you sell on. These sites are often sufficiently optimized that a buyer can find them through a search engine if they are looking for a specific type of product (one good example is real estate). You're much more likely to find a buyer for an item you list on a niche site, than a new site that is trying to provide listings across all categories because they likely are not going to be able to find you interested buyers. So, while these sites may be free, save yourself sometime and try out the niche sites instead. You'll get a better return on the time you spend.