Being security conscious myself, I have been testing several plugins to improve the security of WordPress powered sites. As a matter of fact, I have several post that talks about this subject (ex: http://www.iblogzone.com/2013/06/safety-and-security-for-wordpress-blogs-infographic-and-more.html). Surprsingly, WordFence has got my attention and having scratched just but the surface, I can immediately tell that it is a "rising star".
I have it now installed on several of my sites it is working well. Soon enough, I will be replacing the other plugins I'm using for this one. Just looking into some "other" aspects, just to be 100%. if however you don't have any plugin yet installed, start with this one. Featured packed like no other free plugin I know of.
For the developers, thanks so much for what you do and for the contribution you provide for the community. Kudos...