Since Worm's already been recommended, let me mention another web serial-- Citadel. The first 18 chapters or so are collected in an ebook, "Training in Necessity", available at Amazon.
Citadel takes place years after superpowers began appearing, and unlike Reckoners, the people with powers aren't universally villains. But they are incredibly dangerous, and the world has not dealt with it very well. Large portions of the US have collapsed into feudal rule, entire countries have been taken over by powerful superhumans, and large portions of the planet have been rendered uninhabitable. This is a world where at any moment, some random person somewhere could develop a power that takes out millions, and on more than one occasion, this has actually happened. In what is left of the U.S., the Citadel organization trains superpowered cadets to deal with such threats with a degree of ruthlessness and efficiency more akin to a military organization than superheroes. After the portion covered in "Training in Necessity", the serial follows some of the cadets in their postings after graduation.
I could recommend a long list of graphic novels, but it would be more efficient to point you to this tvtropes page. Some works to which I'd draw particular attention, though:
Np, also looks like citadel has a kindle version on amazon so the reviews might be helpful:
http://www.amazon.com/Training-Necessity-Citadel-Book-1-ebook/dp/B017PJOQDK