I went on a Ciclismo Classico http://www.ciclismoclassico.com trip to Italy in May/June, and it was fantastic, I wouldn't have changed a thing. They focus mostly on Italy, but also do other trips in Europe.

I found this site really helpful when deciding which company to go with:

http://www.biketour-reviews.com/index.htm

It provides participants' feedback on a wide range of bike tour companies, as well as gives insight into the differences between the various (many many) companies.