Justin,
Simplest way do a site search in Google eg:
site:www.seomoz.org.
Navigate to the last page of results - you'll want to change the results to 100 in the search settings if you have a large-ish site.
Underneath the last result it will say something like:
In order to show you the most relevant results, we have omitted some entries very similar to the X already displayed.
If you like, you can repeat the search with the omitted results included.
Press that link. The difference between your standard results and what this shows is most likely duplicate content. Then you just need to find those pages Out of interest does anyone know a tool that scrapes these results and provides a csv of those links, would be handy rather than having to manually check which is difficult at the best of times.
If you have query strings or duplicate links your pretty certain to have duplicate content of some kind particularly in my experience if you have an e-commerce site and you have various categories that tend to cover the same type of products.
