Here is a great way to practice comparing fractions with unlike denominators using the least (or lowest) common multiple method. Cuisenaire Rods help make it visually obvious what we are talking about.
Be aware, though, that this is not an activity for those who have just recently been introduced to Cuisenaire Rods or fractions. This should be done after much play/work with both first so that children understand what the rods stand for.
This game idea comes from the Let’s Play Math blog. Here is the specific post: http://letsplaymath.net/2006/12/29/the-game-that-is-worth-1000-worksheets/