Can anyone recommend a website, book, or simply a list of refactoring strategies for procedural languages as opposed to object oriented languages?
Everything I was able to find contained some strategies that could apply, most were useful only if working in an OO language.
Really? That's odd, as the most basic refactoring concept ("find common code and pull it out into a separate function") works at least as well in procedural code as OO code.
Refactoring isn't explicitly an OO concept. People have been refactoring C code for years. Barring anything that's related to OO (such as refactoring inheritance into composition), the standard stuff applies, e.g., move duplicate code into a single function (as James mentions).
Thinking Forth has lots of really good advice about refactoring. I am also very fond of David Parnas' paper On The Criteria to be Used in Decomposing Systems into Modules.
Take a look at Working Effectively with Legacy Code by Michael Feathers.