I am a trained reading specialist for students in Kindergarten through Grade 12. For younger teenages, I would recommend adventure fantasies such as Rick Riordan's Percy Jackson and the Olympians, The Kane Chronicles, or The Heroes of Olympus. Gregor the Overlander and the remainder of the series by Hunger Games author Suzanne Collins are also favorites of younger teens and tweens. Of course, there are the time tested Harry Potter (JK Rowling), Chronicles of Narnia (CS Lewis), and Inheritance books (Christopher Paloini) have sold hundreds of millions of copies throughout the world. Graphic novels (like the Diaries of a Wimpy Kid) are also taking off in popularity
Older teenagers often enjoy biographies about the famous atheletes, singer/entertainers, and actors or actresses they are interested in. It is a nice distraction from the English and Early American literature they are often required to read in their English and American Lit classes in high school. Magazine subscriptions (ESPN the Mag, Billboard, etc.) also make great gifts for older teenagers, as the articles can be read quickly and related to their interests.