There is no ecommerce site quite like eBay in terms of style, size and scope, but there are a number of smaller auction and ecommerce sites that compete successfully in a variety of categories and niches. (I'm referring to sites that allow third-party sales.) Fortune Small Business did a nice write-up on some of the alternative sites and what they are doing in light of recent seller unrest at eBay.
You can find a chart of online auction sites and storefronts on the AuctionBytes website that give you an idea of the fees at the various sites. What would be valuable is to hear from sellers themselves about their own experiences with eBay alternatives.
Having covered the dialog about this topic for years, I believe that a seller's success on a given marketplace depends on the type of items the sell and volume they do. I'd like to open this up to a discussion of which sites you've tried and the lessons you've learned. Please indicate what kinds of goods you sell since that is an important factor.
What might not be apparent to outsiders is also the challenge of juggling sales on multiple marketplaces. Is it worth the hassle to list on alternative sites? Experienced multi-channel sellers, let us know what you think.
PS: There is no St. Elsewhere on AuctionBytes, you can feel free to mention eBay competitors by name.