I haven't been to Italy with them, but www.backroads.com is a great company (I did a New Zealand multi-sport trip with them). If you aren't interested in actually going with them, you can still get some route and lodging ideas by looking at their website; they have multiple biking trips all over Italy.
We've traveled in Northern Italy for some time, Tuscany is our favorite area, as is for most people. If biking, you might try the Chianti Road, South of Florence, and North of San Gimigiano, which is great place to stay for the week end (see photo of valley from wall around San Gimigiano. Or, take a short trip South to Montepuluciano (see photo of city on hill) from below.