This page contains a growing list of general extortion handling related resources.
Hobbs Act—Extortion By Force, Violence, or Fear
Vexatious litigation (Wikipedia article)
What to do when you are receiving harmful threats from scammers by phone or email
The FBI's Alert Regarding "Sextortion": Why Cyber Blackmail, Though Illegal, Is Difficult to Stop and What Computer Users Can Do
Negotiating with Extortionist Government Functionaries Part 2: Legal, Logical Moral and Emotional Barriers