Some of our favorites:
Pacer Login
http://www.pacer.gov/login.html
Export-Import Bank
http://www.exim.gov/
American Express Merchant Policy
https://www209.americanexpress.com/merchant/singlevoice/USEng/FrontServlet?request_type=navigate&page=merchantPolicy
Mastercard Surcharge Rules
http://www.mastercard.us/merchants/support/surcharge-rules.html
Visa Surcharging Rules
http://usa.visa.com/merchants/operations/surcharging.html
OFAC FREE SDN Search page
http://sdnsearch.ofac.treas.gov/
O FAC FREE SDN Search Information page
http://www.treasury.gov/resource-center/sanctions/SDN-List/Pages/fuzzy_logic.aspx