Poloniex is now the biggest non-Chinese alt exchange since Cryptsy died. It is pretty liquid. Bittrex sadly doesn't have as much liquidity which means orders tend not to be filled very quickly even for moderately popular coins.
Hey thanks!
I hadn't heard of Bittrex.com. It appears they have about 190 coins. That's exactly what I'm looking for. I'm trying to see where Coinmarketcap.com is basing its pricing as they list prices for over 600 coins!
http://coinmarketcap.com/currencies/views/all/Click on the highlighted price of any coin you want. The page that opens gives you more info about the coin and it shows all the markets for that coin.