Who Can You Trust to Test Your Network Security?

sjuels asks: "I am working in a US based company, where we have installed a commercial firewall solution, and now I would like to know how secure we are. I know that a system like ours is never going to be 100% safe from attacks, but I would like to know how vulnerable we are, and I do not trust the company that installed the firewall solution to find the holes in their own product, and the guys that can really do some damage to a system like ours are not exactly in the phone book. How do other people get around this? I cannot believe that it is not a consideration for everyone who tries to secure a network." Anyone out there have recommendations for Security Consultants? Which ones are worth the money that you will spend and which ones should you stay far away from?