DS1 (age 9) has the Percy Jackson books and really likes them. I picked it up one day when it was lying on the coffee table to have a look. Its really good! Ok, some of the plot is a bit weak at times and Percy has a lot more maturity than you might ever expect of a pre-pubescent boy bot WOW! I am actually reading the lightning bolt one now for my own enjoyment (and learning a bit about the Greek Gods whilst i am at it!).
I especially liked the idea that the gates of hell are to be found in Los Angeles!