Greetings to all !
I am a bit overwhelmed by the sheer number of sites offering BTC trading.
What I intend to to is profiting from the volatility of the BTC price in $ or €.
I would prefer a site that allows for instant action, so I do not have to wait for another member to sell/buy at the current price or a slow banktransfer to be executed.
You have numerous options. What you need to think about us that some ask for verification to be done even if you trade just bitcoins, so to say, if you don't wire Fiat to the exchange or withdraw it. Bitstamp is one of these, on the other side btc-e doesn't ask for that.
Also you need to think about the security. Posts above have suggested many exchanges, you need to do a research and use the most secure ones, because believe me, there are many shady ones.
Good luck.