One of the programs I have really enjoyed and that seems to have been very effective is the Prize Buggy Punch Card.
Here's how it works. At the beginning of each month, K-5 students receive a punchcard with 5 slots to get punched. Second through fifth grade students are encouraged to read at least one book from the Genre of the Month as well as an AR book and 3 other books or other media of their choice. K and 1st grade students are encouraged to read 5 of any type of material. After reading each material, they get a punch in their punch card. When they have completed their punch card, they bring it to the Media Center and pick a prize from the Prize Buggy, with the exception of K and 1st grade. They come as a class at the end of the month to the Prize Buggy.
Here's the front and side view of the Prize Buggy. It's really just an AV cart that I decorated with fabric and loaded up with white baskets full of prizes.
Here are some close ups of the prizes.
Here are some pictures of the students choosing their prizes. Even the fifth graders love it!