When to Go?
Basically, anytime is a good time to travel to Italy. The climate doesn't vary greatly making Italy a pleasant trip any season. Then again I'm biased - I spent close to ten wonderful years in Italy and I think it's fantastic all year round. The busiest tourist period is from May through October, leaving the off-season of spring and autumn as the choice times to savor the beauty of Italy.
April and November are to me the best times to go to most places in Italy. During that time the cost, both for airfare and lodging, will generally be lower, and there will be less tourists thundering about.
I fully realize that most people have time off in the summer, but I would counsel against coming to Italy during that time. It is quite literally swamped with fellow travelers. To be able to get a true feel of Italy, especially if you are going to Rome, Venice or Venice, it is best to avoid coming in the summer.
If you do come in the summer, be aware that in August the entire country literally shuts down as most Italians abandon the cities to vacation at the beach or in the mountains.
Naturally all of this depends on where you want to go and what you want to do. However, overall, Italy's climate is rather moderate, helping to make for a pleasant experience any time of the year. If you have any questions about your trip, don't hesitate to send me an email at firstname.lastname@example.org.