I recommend the fisher price roll a rounds too, they're great! DS loves pushing them around the house. I gave him a shallow cardboard box (like the ones from the fruit shop) and he's been having fun climbing in and out, turning it over and sitting on top, putting toys in it etc. If you don't mind the mess some fun ones are letting them splash their hands/float toys in a tub of water or fingerpainting with plain yoghurt coloured with a smidge of food colouring.