Randi has gone after a lot of pseudo-religious organizations and they're still lots more to go before you can narrow it down to Co$.
http://www.vediccity.net/ - An entire city and school bought and controlled by Maharishi Mahesh's Transcendental Meditation organization
The Mormon Church - Self explanatory
Raëlism - Wacked out UFO cult founded by a Frenchman in 1974 with anywhere from 2000-5000 followers globally
Moonies - Sun Myung Moons private church where he claims to be Christ (and about every other major religious character) that owns The Washington Times, Kahr Firearms, and many other companies. Personal audience has been given to a few POTUS
Harold Camping's Family Radio - The guy who predicted the rapture a few times in the past couple of years
Lots and lots of possibilities. Co$ would be interesting for Randi to take on but it would be cool to see him deal with any of the above as well