Core Impact : An automated, comprehensive penetration testing product
Core Impact isn’t cheap (be prepared to spend tens of thousands of dollars), but it is widely considered to be the most powerful exploitation tool available. It sports a large, regularly updated database of professional exploits, and can do neat tricks like exploiting one machine and then establishing an encrypted tunnel through that machine to reach and exploit other boxes. If you can’t afford Impact, take a look at the cheaper Canvas or the excellent and free Metasploit Framework. Your best bet is to use all three.