I have just run across a rhythm app for the iPad called Rhythm Lab. I have only had a few minutes to try it out but it looks pretty good. I plan to try it with my students over the next few weeks.
The app has you tap back rhythms that are on the screen. It can be with one or two hands. This will make it a good tool to improve your sight-reading.
I will try to see if I can find a similar app for Android.