Grammar Girl Podcasts - Grammar Girl presents you with clear explanations of grammar-related concepts in both visual and audio formats, supporting different learners.
Free Rice - If you correctly identify synonyms at increasingly difficult levels, rice will be donated to those in need. The United Nations World Food Program will donate ten grains of rice for each correct answer.
YALSA's Teen Book Finder - "YALSA's Teen Book Finder is a free app to help teens, parents, librarians and library staff, educators, and anyone who loves YA literature access to the past three years' of YALSA's awards and lists on their smartphone." (ala.org)
Figment - You must be 13 years old to create a Figment account.
"Figment is a community where you can share your writing, connect with other readers, and discover new stories and authors. Whatever you're into, from sonnets to mysteries, from sci-fi stories to cell phone novels, you can find it all here." (Figment.com)
Thesaurus/Dictionary.com - Not only will you discover the meaning of words that you are specifically looking up, but you can also learn the WORD OF THE DAY, the history of many idioms, and more! Notice the "Dictionary Decoder" and "Relevant Words" on the home page!