Auditing Active Directory Passwords

[k7.fantr () gmail com]

I am looking for advice for auditing the password strength of passwords in Active Directory. I have used l0phtcrack and 
other such tools in the past against local accounts (SAM and System files) but I do not know what to use for Active 
Directory. 

I do not want to brute force and lock out everyone's accounts, so I would prefer an off-line audit. 

I have domain admin credentials. 

I am trying to build a case to turn on complexity requirements by showing the fact that people do not voluntarily 
follow the password policy (big shock to us, but not to the executive management).

Any tools that would work in this capacity would be greatly appreciated, especially open source or low cost ones.