Lost Heir by E.G. Foley

If you have read all the Percy Jackson/demigod/Kane Chronicles stuff and are looking for another series, this is a good one. (The second book is Jake and the Giant and the third is called The Dark Portal.) Jake is a very likeable character combining a little bit of rough-edged street smarts from his time on the streets with intelligence, bravery and loyalty. Jake's best friend is an Irish girl from the streets. This is balanced by two sheltered cousins- a super-genius boy and an empathic girl who talks to animals. The villian is smarmy and the supporting cast is engaging. 

The next book, Jake and the Giant, was good, but not quite as good. Jake's flaws seemed to dominate the book more and the plot was a little more slapstick. There were numerous scenes of Jake and his cousin playing matchmaker for a giant that felt like they were just there to make the book silly. That aside, it had some great bits and I learned a lot about Norse mythology. (The chief foe is Loki.)