I am a huge fan of the Harry Potter books, and this series by Rick Riorden has come pretty close to that level of enjoyment for me. They are a series of books about a young unlikely hero--Percy Jackson, son of Posiedon. Following adventure after adventure, you find yourself brushed up on your Greek mythology and thoroughly entertained into the bargain. They are well-written with a hip (but not really disrespectful) teenage voice to them (written in first person), and the dialogue is totally believable. I thought each book in the series improved upon the one before it.
