jBidWatcher is a Java-based application allowing you to monitor auctions you're not part of, submit bids, snipe (bid at the last moment), and otherwise track your auction-site experience.
Currently it is only implemented for eBay, but it is abstracted suitably to work with any online auction site with a minimum of changes.
It is under active development, and issues are quickly responded to. Bug reports and feature requests are always welcome, as are praise and complaints.