Rhythm Blocks have been a big hit in my studio! I have added level two for some more complex rhythms.
We have been building rhythms with blocks based on the time signature. One added benefit in using the blocks is they transfer well from the floor to the keyboard. My students can make a rhythm on the floor and then take there blocks to the keyboard to play them using notes or chords. This has been a great hands on activity.
For more ideas see Rhythm Blocks Level One
Google Docs: Rhythm Blocks: Level Two