Percy Jackson and the Olympians: The Lightning Thief
by Riordan, Rick
Hyperion
2006
ages 8-12
paperback

The first book in the Percy Jackson series.  One of the best middle grade series out there...  funny, exciting, fantastic.

Percy finds out in the first one that he is Poseidon's son and must go to a camp on Long Island to learn to battle mythical monsters.

I know both a 7 year old and a 35 year old who call this their favorite series, and many more in between and on both sides.