View the full text of more than 7,000 textbooks on your iPhone — for free. CourseSmart makes its money through the licensing of e-textbooks, which expire after a certain access period, typically about 180 days. The books cost roughly half as much as their print equivalents, although there's no way to resell or keep the books past the subscription period. As for the virtues of reading textbooks on the iPhone? Well, you need sharp eyes. But with persistent rumors of an Apple tablet computer coming in the near future, CourseSmart is likely a harbinger of reader applications to come. (CourseSmart, free)