I bought the AA Essential Guide to Florence earlier this year and found it very useful on my trip there. I plan to go to Venice early next year and I'm sure this guide will be very helpful when I'm there, these books contain loads of useful information yet are small enough to carry around with no problem - looking forward to using it.
This was the only small guide book to Verona that I could find. It seems to cover everything pretty well and has useful maps for getting around. Also has brief details of nearby places including Vicenza and Lake Garda.