Thanks for the response. I'll take a look at Password Policy Enforcer as well. Having read through your website, I can see why you'd recommend SpecOps rather nFront - I'll be checking on performance impact as part of my evaluation.
Checking passwords is a trivial task for a modern computer. None of the rules should have a noticeable performance impact except for the Dictionary rule. It's only when you are searching through a few (or a few hundred) megabytes that it will make a difference.
Good luck with your evaluation, I hope you find a product that does exactly what you want.