There are several bus tour companies in Savannah. We chose the Gray Line company (red trolleys) because we could get a free entrance to the maritime museum by buying our ticket there. A bus tour is the best thing to do if you don't have lots of time for sightseeing because you'll learn a lot quickly. I also would recommend it as the first thing to do if you do have more time because you can learn a little about everything and choose what you want to learn more about, then using the on-off feature to get around. We bought our tickets pretty late in the day, so they let us do the full 90-minute tour that day and then save our ticket so we could use the on-off feature the next day. This was excellent because they stop running at around 4:30pm.
The tour guides were nice and gave lots of neat information about all of the things in Savannah.
The next day we toured the maritime museum, which has lots of models of ships from Savannah's history. We also toured the Andrew Lowe house, which was one of the choices for a tour when you bought your ticket. If you're interested in a particular house, make sure you note which days its open/closed when you purchase your bus ticket! This was a nice, relaxing way to fit lots of sightseeing into a small amount of time.