Hogenakal falls in Tamil Nadu, 180+kms from Bangalore, is my favourite one around. There is not one, but a series of waterfalls all around a rocky terrain.
you hire a coracle to take you across the river to the view-point of the falls, and then again right below the waterfalls and to a point where you are dropped off for a while...you got to climb a hill and whoa! some more rocks and mind-blowing waterfalls. back down. and the coracle drops you off at a sandy bank at the far end where the water's quite shallow. splash around and the coracle takes you back after an hour or so. you get to see an ocassional kingfisher, and lots of cattle egret and the pond heron picking tiny fishes at the waterfalls.