This is a site comparing exchanges, but it does not state how trustworthy an exchange is:
http://coincompare.com/Of course you can assume you can trust the exchange if it has been online for a few years and it has a high volume. That suggests people keep using the exchange and they won't do that if the exchange is stealing coins.
Another idea is to start this kind of site yourself. Maybe you can even make some money with it
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)