Etherdelta I guess. Plenty of coins, solid volume, working well for a long time, the only downside actually is their awful website. But you get used to it.
Etherdelta only allows you to trade coins versus Ethereum, and that's it. No BTC/LTC, BTC/DASH, etc. It's too much of a limiting factor, but I do agree that the volume it's generating is very decent for a decentralized exchange platform. Other than that, most of the well known decentralized exchanges are already mentioned here, except for coinffeine. It's a decentralized exchange that has been growing for quite a while now. It may not yet have impressive volumes, but we can't expect them to be anywhere near the centralized exchanges. People looking for decentralization have to accept less convenience and less overall usability.
