"Bigot" wasn't a clearance level, it was an additional layer of security along with clearance levels. A clearance level like "secret" means it requires people viewing it to have passed a security check of the appropriate level.
In addition to having the required security clearance for the information (which could be any clearance level) you usually have to be approved to see that specific information. Thus, the "Bigot List". Today it would be called sensitive compartmentalized information or special access programs many, many of which exist within various government departments.
Rather than have people walking around with blanket security clearances who can potentially know too much about too many things, special access programs add a layer of security by ensure that the fewest people possible know only the secrets they need to know. Compartmentalization is a powerful security measure. This has often been referred to as "need to know" or (inaccurately) "above top secret".
There were many other programs like this. "Bigot" was the name for the list of people allowed to know details of Overlord. @o.m. already mentioned Magic (intelligence coming from a US code breaking project) and Ultra (intelligence coming from British GC&CS). Any major operation would have its own secrecy and deception plan. For example, Operation Overlord, the invasion of France, required a great number of compartmentalized information both to keep the time and location for the invasion a secret and for their deception plan, Operation Bodyguard which included Operation Fortitude.
Whether they had additional code names beyond the operation name, I don't know.