Esoteric cults or groups who have secret information that is not revealed to people outside the organization. 


Access Consciousness
The Brethren (Jim Roberts Group) - A very secretive sect of nomadic Christians, who eat out of dumpsters and forbid laughing and playing (1971 - present)
Christian Assemblies International cult - A fundamentalist church that was caught running a secret homosexual sex ring
People of Praise
Plymouth Brethren Christian Church (Exclusive Brethren)