Analysis of the DAO exploit - Hacking, Distributed
Really in-depth and fascinating look at the details of the exploit. This is the best article I've read that gets into the minutia.
This post will be the first in what is potentially a series, deconstructing and explaining what went wrong at the technical level while providing a timeline tracing the actions of the attacker back through the blockchain. This first post will focus on how exactly the attacker stole all the money in the DAO.