Hmmm.. While in Rome you want to see (not in order of importance) the Trevi Fountain, the Spanish steps, the Colosseum, the Vatican museum(better bring some bengay because your neck will be hurting from looking up all the time)(also remember, flash photography is prohibited in the museum, and all photography is banned in the Sistine Chapel so if you want to take a picture of "the origin of man", you better be sneaky and fast because they are always watching), St. Peter's Basilica (don't use flash photography to photograph Michelangelo's Pieta as it is behind a wall of glass and the picture will look a little strange), the Forum near Palatine Hill, Saint Angelo's castle (built by Hadrian and offers great views of the city), the Pantheon, Piazza Navona (has Bernini's "Fountain of the Four Rivers"), the Ponte St. Angelo (a gorgeous bridge over the Tiber River right in front of St. Angelo's castle), and when you are ready for some good food and gelato, just head to the Campo dei Fiori which is about a 3 minute walk from the Piazza Navona.
These are just things to see in Rome. I will let someone else do the Florence sites so I won't have a full page post. Good luck and wear comfortable shoes.