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Bittrex is one of the larger crypto to crypto exchanges offering a large number of trading pairs into bitcoin - including all the major cryptos such as blackcoin, ethereum and litecoin. They also offer NeuCoin and Ethereum.
The exchange does have a very high turnover crypto currencies - leading some to accuse it of allowing pump and dump schemes that erode confidence in the crypto currency ecosystem as a whole. Apart from that they do have very good security with two factor authentication and are United States based.