The Sea of Monsters / Rick Riordan
Camp Half-Blood is in trouble. Its magical boundary has been weakened with poison and uninvited monsters are starting to get in. Not only that. Percy’s friend Grover the satyr has been captured and is being held by a monster who wants to marry him. It turns out that the solution to both problems is the same. All Percy and his friends have to do is sail across the Sea of Monsters, also now known as the Bermuda Triangle and rescue Grover and the Golden Fleece. Unfortunately seas full of monsters, old enemies and titans are not all that easy to cross.
Rick Riordan's series about Percy Jackson & the Olympians, which starts with The Lightning Thief , is an exciting mix of fantasy fiction and classical mythology. If you enjoy the series, here's the start of another one that you may enjoy:
 Pandora Gets Jealous  / Carolyn Hennesy
In ancient Athens, Pandora, the thirteen-year-old daughter of the titan Prometheus, and her friends Alice and Iole have to bring in something special for tomorrow’s big school project, “The Enduring Presence of the Gods in Our Daily Life.” Pandy thought about bringing in a piece of her dad’s liver again, until the other girls begged her not to. But chasing her little brother around at home she discovers an odd metal case with a small bronze lock and inside that a smaller wooden box: old but smooth with only a wax seal keeping closed, the great seal of Zeus. A box containing all the misery in the world, with the seal of Zeus— surely this will get her an alpha on her project!
And you might also like to try some modern versions of the original myths:
 Greek Myths  / retold by Ann Turnbull ; illustrated by Sarah Young
This is a fresh retelling of stories from classical Greek mythology, using early versions of the myths. Trumbull tells, “a mixture of nature myths, hero tales, and stories of the struggles between gods and mortals. Instead of the usual arrangement by theme, she groups all the stories about a single character together,
 Adventures of the Greek heroes  / Mollie McLean & Anne Wiseman; illustrated by Witold T. Mars
This well written simple text retelling of the adventures of Hercules, Perseus, Theseus, Orpheaus, Meleager, and the Argonauts makes classical mythology accessible to beginning readers who are up to the challenge of a longer than average chapter book. It includes an index and pronunciation of names.
And here’s a monstrous bonus book:
 The Cyclopes / Russell Roberts
This is a short, very informative and colorfully illustrated book about the one-eyed monsters of classical mythology. Roberts retells the encounter of Polyphemus with Odysseus and his crew from the Odyssey and the giant’s frustrated love for the nymph Galatea from the Metamorphoses. He also tells of other cyclopes that aided Zeus and Hephaestus.