SI love power towers. Basically, they are bathroom cups with a sight word to read or a math problem to do. You store them in a Pringle's can. The students stack the cups once they answer the question. I put the answers to the math questions inside the cups.
The problem with these are when 2 or more students are using them and they get mixed up. You can use different cups for each power tower. I put the colored garage sale stickers on each set. This way the students just match the color. Easy cleanup!