I was going to say Hennig and Savage as well, and it turns out that's the consensus.
I'm just going to throw out some others I think were great IC champions, and might fly under the radar a bit. I don't know if anyone would classify these guys as the greatest, but meh, I think they should at least be in the discussion. Also, nobody who was more remembered as a top champion in the WWF/E.
80's: Don Muraco, Pedro Morales, Tito Santana
90's: Jeff Jarrett, Razor Ramon, Owen Hart, Goldust
2000's: Shelton Benjamin, RVD
I don't know if we'll get anymore great IC champions anymore since the company's changed so much. The title's barely even on PPV and it kinda sucks. I'm in favor of them retiring the title again and bringing in a gimmick title of some sort (Hardcore, TV, Six-Man.) than have them sully it with a Santino or Hornswoggle reign or something.