Children 12 and under can earn a free $3 gift card to Half Price Books each week they read (or are read to) for 15 minutes at least five days. They often have books for less than $3 in their clearance section which will result in a free book per child each week!
This program runs through July 31, 2009. See more details .
Also, if you're going to be heading into Half Price Books to pick up your free gift cards, you might also consider bringing in some of your extra books or magazines to sell to them for store credit or cash. I've heard they have pretty reasonable rates and it's a great way to get rid of things you no longer need or use in your home and earn a little extra cash while you're at it!