The whole series, really. The main character, Miriam, is a strong, kick-ass heroine, without the book ever making her gender the reason for her awesomeness.
However, it also deals with gender issues (as one of many plot lines) – Miriam finds out she’s the long-lost heir to a massive fortune in a parallel world. A medieval-type world, and a family that firmly believes a woman’s role is to get married to the appropriate man and make babies to continue the family line.
Miriam shakes things up in brilliant ways that are nevertheless realistic, and don’t trivialise the struggles that she faces in dealing with scheming, power-hungry nobility that has no interest in changing it’s ways.