Several units could fit your needs. What are you looking to get out of it or a price range your looking at?
You said ponds so GPS would not be needed but 2D with DI is also a option unless you just want a 2D unit. Without know a price range, take a look at the Humminbird portable PiranhaMax 160-175-230 models. Comes with a suction cup transducer and self contained.
Another option would be the HB Fishing Buddy, just clamp it on and off the side on the boat. Higher end, most of the reputable makers have several that are self contained and are used on ice but you can get a TM ducer to run on the boat. Lowrance has one of the brightest screens I've seen in the 4x and a great unit. Hope this gets you started and good luck on the water