Over the years, I have taken many a delightful tour with AvventureBellissime. Each one has introduced me to a part of Venice that I might never have discovered on my own. Recently they have updated their website and added a great feature. You can go to their YouTube channel (http://www.youtube.com/user/AvventureBellissime/videos?view=0) and see a brief video of their tours. A great way to spend a day when you're dreaming about being in Venice!
This photo is from a private Venice Secret Gardens walking tour. Highly recommended!