Along with some friends I've built the Wyvern Exchange, a decentralized exchange for nonfungible Ethereum assets (not tokens) - think CryptoKitties, ENS names, or even Ownable smart contracts themselves. Using the Wyvern Exchange, you'll be able to buy or sell any asset that you can send in an Ethereum transaction without trusting your counterparty (whomever you're buying from or selling to) or us (the developers).
We're finishing an audit this week and launching on mainnet as soon as the audit is complete - and we'd like to know what assets the Ethereum community would like to be supported (I've already lost track of the number of CryptoKitties clones). If you can send it in an Ethereum transaction, you can buy or sell it on the Exchange - so, if you have a suggestion, please submit it to our asset schema repository or just comment on this post.
Also glad to answer any questions about the project in general - fire away!