Ubiquiti's EdgeRouter gets my vote if you're willing to muck around on the CLI to get to advanced features.

I'm sure you can get it to run on some computer that act like a router or grab some embedded stuff.

I haven't tried it too much work. But openBSD is solidly crazy. They sacrifice performance for security and security is always the first thing on their mind and anything else are distant second. They code review too.

http://www.bsdnow.tv/tutorials/openbsd-router#hardware