OpenBSD : The Proactively Secure Operating System
OpenBSD is one of the only operating systems to treat security as their very highest priority. Even higher than usability in some cases. But their enviable security record speaks for itself. They also focus on stability and fight to obtain documentation for the hardware they wish to support. Perhaps their greatest achievement was creating OpenSSH. OpenBSD users also love [pf], their firewall tool.
Bastille : Security hardening script for Linux, Mac OS X, and HP-UX The Bastille Hardening program “locks down” an operating system, proactively configuring the system