has handy interactive maps and pictures of the falls. Most of the best ones are in northern Wis and the Upper Peninsula of Michigan. Not exactly nearby, but if you wanted to make a 3 day trip, you could probably see 20-30 of them. Many of them are not huge in size, but they are very scenic.
We did a trip like that last year - it was lots of fun. Make sure to print the maps out before you leave - the UP can be skimpy on cell reception. One or two of them may require some moderate bushwhacking to get a good view, but most of them are easy to get to.