People Rhythms are one of my favorite ways to help kids with visualizing rhythm. What I have found is kids have a really hard time understanding that eighth notes are 2 sounds on one beat and this, plus repeating the definition, really helps.
I have a stack of carpet squares that I picked up from a design center that was closing. They were completely free and I use them all the time; sometimes for a friend who needs a defined space to stay within, other times for bass xylophone players to sit back on between songs. There are many options but I always have a set of four at the front of the room for rhythm activities.
Recently, we used them to discover two sounds on a beat. I play the rhythm of the words in a song that we are working on (this time Big Black Cats from First Grade Game Plan) and lead the kids in discovering the rhythm. I allow students to come up and gently rearrange the rhythm until we have matched it to the song. The kids love being a part of the people rhythm and reading people rhythms.
I have also used these carpet squares for carpet rhythms.