Wikipedia has a pretty decent write-up with references.
Specifically to tomatoes, it says:
Significant changes occurred with the discovery of the New World with the introduction of items such as potatoes, tomatoes, bell peppers and maize, now central to the cuisine but not introduced in quantity until the 18th century.
As far as not-in-quantity, the Wiki's source article states:
Another staple of Italian food is the tomato. It was introduced to Italy in 1522 by the Spanish, who ruled over the kingdom of Naples. They had picked up the tomato in Peru, where it was known by the Mayan word xtomatl. (Although if you ask Neapolitans, they'll tell you that Neapolitan sailors brought the tomato into port themselves.)
Basil (aka St. Joseph's Wart) - not sure how it came to Italy, but it spread from India a long long time ago and was known both to ancient Egyptians and Greeks of early Christian times, if not before; as well as Ancient Romans). However, Basil was thought to be unlucky, bad for you (I especially love the "scorpions in the brain" theory) and all-around evil till at least 17th century.