I use the Humminbird SmartCast RF-30 Wrist Sonar. Got it for $80 right after it came out.
For those who aren't familiar with this: You put a watch on your wrist that is the reciever/display. Then you put the sender on a pole and cast it out to the area you want to fish. It floats on the surface and sends a signal back to the wrist watch. Very cool.
I have a friend who calls it, "Dick Tracy."
It works well in most situations but the electronics aren't real fast. By that I mean if you cast the sending unit into a medium speed rapid it can't get a good reading because the bottom is going by so fast and the unit is bouncing in the rapid.
Also, I have noticed that you have to wipe off the metal contacts on the sending unit between each cast. They sense when the sender is in water and turn it on. If you don't wipe off the contacts they get crud on them and the sender doesn't turn on.
I use it from my pontoon boats. It did result in one chinook hookup last fall but I didn't get the hook set very well and lost it.
It was cool because I knew exactly where to set the depth on my bobber. The bite was within seconds of casting to the fish. It happened so fast that I wasn't ready.