It seems somewhat sacrilegious to think of visiting Rome without touring the colosseum and ancient forums. Now it's possible to tour the city as it looked in 320 AD without ever leaving home. Google Earth has created a 3D view of the city that allows you to fly down to see famous buildings and monuments. Click on the monument and get a complete description of what it was and what it was used for. This incredible tool is a great precursor to visiting Rome, or a wonderful advantage for those who may not have the opportunity to get there.
For a free download of Google Earth, go to earth.google.com/rome/. Here is a preview of what you'll find: