One app that we use is called Monkey Drum, and it is a free app that has a fun cartoon monkey who mimics what you do on the drum. The kids play a beat or rhythm and he plays it back. We'll use this later in the year when we work on rhythms as well. They LOVE playing this app and coming up with super long rhythms and beats to get bananas for the monkey!
I also use Magic Piano by Smule in music as a fun extra activity with all grade levels. Not only is this app musical, but it helps with listening, hand-eye coordination, and even counting! It is a lot like guitar hero where the students press their finger as the dots pass by, and even the first graders can be successful at the easy levels.
Here we are playing Magic Piano and you can see how the class is "practicing" in the air or on the floor behind our player.
Here is the cute Monkey from Monkey Drum on the big screen playing one of the students' beat.
Here, a students is watching the monkey play his rhythm.
The Monkey is patiently waiting for this student to play his rhythm on the drum!