Wasn't 4E code-named "Orcus"? Did 3E have a codename?
Incubus--it's the 'sexy' choice.
Intellect Devourer would be a poor choice.
Issek of the Jug--Oops. Don't own that copyright any more.
Imp. Probably not grandiose enough.
Icarus.
I think it would be great if they called it Iuz or Ivid, but I don't think anyone at WotC knows what Greyhawk is.