TopTenReviews has recently released a '2007 Online Auction Sites Report'. The report gives a detailed review of and rating for top ten leading online auction sites.
Needless to say, eBay topped the review, followed by Overstock and Yahoo! Auctions. Other sites like Amazon, ePier and uBid are in the list too. The report compares and reviews seller fees, process flow, features and benefits, help and support etc, of each online auction site.
If you are considering an eBay alternative, I strongly suggest you to have a look at the wonderful report before making your move.