Seems as though East Hampton's tween-age readers are still enjoying the author's Percy Jackson and Kane Chronicles series. You might also like to make some summer reading time for the Heroes of Olympus series which picks up where Percy left off. The only downside is you will have to wait until fall 2012 for the third in this five-book series.
In the mean time, you can check out Disney-Hyperion's Greeks vs. Romans web site where you will be asked to decide "Whose camp are you in?" Check back often because right now there's not much there... there. Also have fun on Riordan's author site.
Here are but a few graphic novels, non-fiction, and fiction selections for kids and tweens; try these others about mythology and adventure.
Mount Olympus Basketball by Kevin O'Mally [Graphic Novel]
Destiny's Call : the Legend of Perseus by Ryan Foley [Graphic Novel]
Medusa Jones by Ross Collins
Jason and the Argonauts by Dan Whitehead
The Fate of Achilles by Bimba Landmann
The Greeks by Michael Kerrigan
Greek Myths by Eric Kimmel
Greek Hero by Mick Manning
Tales of the Greek Heroes by Roger Lancelyn Green
Olympia : Warrior Athletes of Ancient Greece by David Kennett
Dusssie by Nancy Springer
Iris, Messenger by Sarah Deming
Tales from the Odyssey