This website allows users to create tax return data reports by zipcodes and areas.
Indiana Department of Revenue
Contains current and earlier tax forms back to 1995. Also, information on how and when to file.
Internal Revenue Service
The IRS site contains all of the tax forms back to 1990, the complete tax code, and lots of helpful information for individuals, businesses, professionals, etc.
FAQ's about taxes, history of taxes, federal debt history.