U.S. Secret Service
Founded in 1853, the United States Secret Service existed solely to prevent the creation of counterfeit money. According to the service website, the organization has currently evolved to handle two purposes—"protection of national and visiting foreign leaders, and criminal investigations."
This site provides very little which is directly applicable to the history classroom. However, the site deserves to be recognized in this listing regardless.
If you're interested in the organization itself, the timeline of Secret Service history is a natural place to start.
The service also offers a short section on monetary history.