I've been to Italy. Fine food and finer women.
There's no need to worry about a visa if you're an American citizen and you only intend to stay for tourism.
Remember the following though:
- It may change if you intend to stay for longer than 90 days
- You may be asked at the border to provide documentation of your length of stay (i.e. A return ticket) and proof that you have the money to be self-sufficient
Here is a good website to check for any nationality to check if they need a visa to enter Italy or not: http://www.esteri.it/visti/home_eng.asp
p.s. Watch out for the street vendors that pitch up next to tourist attractions. What a rip off! And the entire city of Florence too