This site is a good introduction to the monuments and history of the Roman Forum made by high school students in Holland.
http://hyperion.advanced.org/11402/#Roman%20Forum

An exhibition on the history of the Vatican at the Library of Congress
http://www.ncsa.uiuc.edu/SDG/Experimental/vatican.exhibit/Vatican.exhibit.html

A site called In Italy with much useful and interesting information and a multitide of links to more useful sites.
http://www.initaly.com/regions/latium/latium.htm

A useful guide to Rome's museums.
http://www.romeguide.it/monum/musei/museiin.htm

This site has information about monuments.
http://www.romeguide.it/monum/indexin.htm

A site on the gardens of the Villa d'Este at Tivoli made by a student at the University of Virginia.
http://www.people.virginia.edu/~mai9e/#Villa%20d'Este

This site for Professor John Pinto's class on the city of Rome at Princeton is based on Nolli's 18th century map of Rome.  One can click on sections of the map and search for individual buildings.  There is a wealth of information, although the slide images can only be used on the Princeton campus.  http://www.princeton.edu/~images/nollistart.html