Keeping tabs on competitive emails is a tricky business. We just completed a competitive email audit, and had to subscribe to many email programs, and then monitor them over 60 days. Well, the Three Minds @ Organic blog posted about an interesting new resource that could help make the process easier... The Newsletter Archive.
It's not the most comprehensive resource, but for a quick dig into a particular industry or company, it looks like it could shape up to be a good tool.