Surfing the web, I have found a document concerning the undocumented cisco commands.
The document is write by Lars Fenneberg (CCIE #7325) and it’s quite old (last revision in 2005).
Certainly this is not a complete list, but I suppose that could be funny to discover some new commands…
I have tried to found other document more exhaustive with no result.
The original document can be found on http://www.elemental.net/~lf/undoc/