Apple's QuickLook is a great service. I have grown to rely upon it a great deal during my daily work. Strangely, Apple seems to have reduced the number of content types that QL can render in Mavericks (e.g., flv), but that's another topic. This note describes how to get QuickLook to display the contents of unknown files as text.
QL handles content specific rendering via what it calls plugins. If a plugin exists for a file type, then QL can generate and display a preview of the file. If one doesn't exist, then you are left in the dark.
There are many file types (e.g., python, restructuredText, etc.) that QL unsurprisingly doesn't handle, but for which it would be highly useful to see contents rendered simply as plain text. I ran across a plugin called QLStephen (https://github.com/whomwah/qlstephen), which does a nice job of exactly this.
It is available via macports, which is how I've been using it. It's so convenient to be able to see inside most files that QL otherwise ignores.