I use BTC-e. I trust them 100%.
https://btc-e.comI have never had a problem there and I actually fucked up, sending a shitload of BTC to a NMC address (thanks Window's Clipboard) and they were able to send them to the right place for me in the end.
They saved my butt and I am always grateful for that.
Their security is also top notch. I like the email confirmation for withdrawals as well.
(transfers out of the exchange are frozen till you get a confirmation email and click the confirmation link etc. Email address can not be changed)