Here are some magnets I made for different rhythms. The length of each magnets corresponds to the number of beats (one beat = 6 inches). I also color-coded the background of rhythm by the number of beats represented (which matches the rhythm bulletin board). This will be a very visual way to see the relationships between different rhythmic values and to create measures with different note values.
The documents have the rhythms already spaced out--just cut on the line (or cut it slightly smaller than the lines to make room for a colored border). The longer values (whole note, dotted-half note, etc.) will need extra white paper on either end to make them the corresponding length. Then, after laminating, I just cut strips of adhesive magnetic sheets to finish them off.
I'm able to use these on the white board or on my teacher desk, as both are magnetic.