Most of the strength estimators I've used allow for a list of common passwords, but I've never seen one that checks against rainbow tables, presumably both beca

Most of the strength estimators I've used allow for a list of common passwords, but I've never seen one that checks against rainbow tables, presumably both because that would take a long time (and enormous resources on the server side -- rainbow tables are big!) and because, absent careful salting, the nature of a rainbow table would guarantee a positive result.