By far the nicest way to explore Bodensee (Lake Constance) is by ferry. There is an extensive network of ferry routes crisscrossing the lake, which services a limited number of towns on the Swiss side as well as many more towns on the German side.
Konstanz is the hub of BSB's network, and other larger towns such as Meersburg and Friedrichshafen have frequent ferry services, whereas smaller towns and those at the extremities of the lake are not serviced as often.
However, bear in mind that it is a large lake, and travelling by ferry is much slower than making the same journey by road - for example, Konstanz to Lindau (which is pretty well end to end) will take you about 3.5 hours.
The weblink below is the BSB timetable for summer 2010 - unfortunately this is currently only available in German, but much of it should be pretty self explanatory. The website promises that it will be available in English in 'a few months', but I have no idea if and when this promise will be delivered on.
The same website also gives fares: return tickets cost double the single fare. If you are going to be in the Bodensee area for some time and plan to take a number of ferry rides, it's worth enquiring about passes - when we visited in 2005, we bought a week pass, which saved us quite a lot.
A passenger/car ferry is available to transport you and/or your vehicle the 4.2 km across the Bodensee (Lake Konstanz) between Konstanz and Meersburg. It is a 15 to 20 minute ride and a ship departs from each side at least 4 times every hour during the day and once per hour at night.
The private car and passenger ferry line across Lake Constance to and from Konstanz makes for a nice interlude in a day of sight-seeing. It's a quick trip, only about 15 minutes, and not expensive, either. Also very convenient, crossing numerous times each hour during the day and once per hour at night.