Rachel- watch the "Stomp Out Loud" video if you can find it- it's got some great examples of rhythm patterns ranging from easy to complex. I have done some of the ball-bouncing and recycled percussion activities with grade 5, but they would apply to older kids as well.
Create "rap" rhymes (I can't believe I'm saying this!) and have the kids notate them. You'll have to notate the first simple ones, and you'll want to teach dotted and syncopated rhythms as soon as you can. Good luck!