@riotdesigners -- Game design: book suggestions

I was wondering if there's any reading material out there on game design that Riot's designers could recommend. Just looking for some ideas/suggestions for books or similar to expand on game-design systems, approaches, techniques, maybe even programming.

Asking you guys because you're in a very specific niche of game design, the kind where you continuously update and evolve your game. Not many companies out there push out a new patch for their game every two-three weeks with changes that could significantly affect the pro scene as well as casual play. So if anyone has a good grasp of solid, evolving and balanced game design, it would be you.

Cheers in any case!