What are some books similar to the Percy Jackson series?

(quote)You can find books like the Percy Jackson series that Rick Riordan recommends on his site: www.rickriordan.com(quote)

There are also two more series by Rick Riordan, The Kane Chronicles (First Two Books out already) and The Heros of Olympus (Again, book one and two out). There will be three for each in all.

Other books that are in the realm of fantasy that may interest you are Lord of the Rings and Harry Potter. HP has a lot of fantasy world stuff.