DD will do the hand motions to Twinkle Twinkle that they do at school. That includes opening and shutting her hands, tapping her temple (for "how I wonder what you are") and attempting to isolate her index fingers and thumbs to create a diamond shape. She will also "sing" along with us, in the right patter.
There are now times that she'll be rhythmically babbling and we'll notice she's doing the hand motions so we know she's singing to herself.
Also last night, for the first time at home, we played "roll the ball" for a good 15 minutes.