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I'm looking for online articles or printed publications that discuss the different aspects of designing a Fail Safe system. I know there are fail safe sensors, redundant safety systems, etc. But what I'm looking for is wiring and program logic practices for creating a fail safe system for inputs (sensors) outside of safety etc... i.e. every day prox or photoelectric sensors, etc.

You need to know how a system (consisting of hardware/firmware/software) may fail (to perform) to design a fail-safe system. Generally FMEDA report from manufacturer is a good help. With increasing awareness of industries toward "functional safety", manufacturers are also forced/encouraged to publish product specific FMEA/FMEDA. Contact vendor or you may refer "www.exida.com" for limited available reports.

Alternative is to fallback on various handbooks to collect failure data/probabilities which are mostly generic and not vendor/model specific.

The website "http://www.safetyusersgroup.com/" is good to start with understanding concepts of functional safety.

Regards.