For my trip to Spain I chose two books to read on the plane. One wasn't that great so I left it behind. The second had a few flaws but it's a good start for younger readers.
The Seer and the Sword by Victoria Hanley. King Kareed of Archeld conquers Bellandra, despite their magic sword that is supposed to make their kingdom invincible. As part of his spoils of war he brings home the son of the defeated king. The boy, Landen, is given to princess Torina as a slave. Her first act is to free him, earning his gratitude and later his love. But Kareed has put his trust in the wrong commander, and Torina's own peaceful existance is soon destroyed.
Pros: good writing, interesting characters, well developed world wherein each kingdom has their own customs and leadership style.
Cons: lots of coincidental situations to move the plot along and given the time frame of the book the characters are less well developed as they might have been otherwise. It's definitely written for teens or even younger readers, who won't mind or notice the flaws as they get pulled into the story of a princess trying to survive in exile.