It might not be "perfect code", but I find it fascinating what certain institutions do to create bug-free and easily testable code, institutions which are involved in work where small errors can quite literally ruin billions of dollars of investment.

For example Coding Standards from NASA's Jet Propulsion Laboratory (JPL) for C[1] and Java[2]

This will also give you an idea of just how tedious it is to do so

I am not even sure if enforcing those strict standards leaves a Turing-complete language

[1] http://lars-lab.jpl.nasa.gov/JPL_Coding_Standard_C.pdf

[2] http://lars-lab.jpl.nasa.gov/JPL_Coding_Standard_Java.pdf