Here a couple of suggestions. I have put together for those who have a limited time in Rome and want to see as much they can on a guided tour!

Option 1

Vatican museums (Sixtine Chapel),  St. Peter's basilica, Colosseum, Forum

 

Option 2

Trevi Fountain, Colonna Square,  Pantheon| Ghetto, Teatro di Marcello, Capitol Square, Forum, Colosseum