The Little Miami is 2 miles from my door.  I visit often.  If you go during the week it's amazing how few people you see being so close to large metropolitan areas.  The river in the upper half is only 30-40 feet wide - a beautiful river and easy canoeing, no rapids to worry about.  If you like to fish you can catch sunfish, rock bass, carp and an occasional smallmouth.  There are a few places along the river you can camp.  There are a number of good canoe outfitters as well.  Weekends are busy - go during the week and you will be pleasantly surprised.