The story of Percy Jackson's lost little sister: Raven Jackson and her adventures. May not seem like Kane Chronicles is connected in the first few chapters, but it will come up. (Will not be finished before Blood of Olympus comes out.)
This is a tragic love story between the Thief Lord and Lora Jackson, a young Assassin. I couldn't put three crossovers, so I'll just tell you, the other crossover is The Children of the Red King series.