My "OMG Loved it!" favorites:

• Harry Potter Series by J.K. Rowling
• Inkheart Trilogy (Inkheart, Inkspell, Inkdeath) by Cornelia Funke
• Looking for Alaska by John Green
• The Outsiders by S. E. Hinton
• A Separate Peace by John Knowles
• Lord of the Flies by William Golding
• The Boy in the Striped Pyjamas Reader by John Boyne
• The Wind Blows Backward by Mary Downing Hahn
• Kidnapped by Robert Louis Stevenson
• Anne of Green Gables Series by Lucy Maud Montgomery

Worthy of a mention:

• His Dark Materials Trilogy (Northern Lights/The Golden Compass, The Subtle Knife, The Amber Spyglass) by Philip Pullman
• Stargirl by Jerry Spinelli (I haven't read the rest of the series yet)
• City of Ember by Jeanne DuPrau (I haven't read the rest of the series yet)
• The Catcher in the Rye by J. D. Salinger

Read but wasn't thrilled with:

• Inheritance Cycle by Christopher Paolini
• Twilight Series by Stephanie Meyer