If you don't like to give a bunch of class levels, dragons are an easy, out of the book villain to go with. They're intelligent, can scheme for all sorts of things, have access to lots of wealth to (potentially) hire mooks, or so on.

The only thing to keep in mind is that while evil dragons are generally murderous and greedy, they also have plenty of reasons they might talk with people instead of just kill them. They basically hide their lair away, but could easily be motivated to do just about anything that would motivate a humanoid villain.

Of course, this still requires you to do something like draw up a general mook hireling in your notes, or such, but generally such people are powerful mostly in large numbers and don't have more than 1-4 levels.