Program in C?  (Without using IDE, etc)

I guess we're in violent agreement. You're basically looking for instructions on how to use the arduino libraries (and hardware) with a more traditional AVR development environment (WINAVR, etc.) As far as I know, no one has written anything along those lines. It'd end up being somewhat different for linux/macos/windows; there is a substantial possibility that the needed compiler versions (ie to support ATmegs328p) are not yet packaged in the binary distributions. Which OS are you using, anyway?

I've been a C programmer for 20+ years, and an emacs bigot for quite a bit longer, but I still find it useful to have the Arduino environment be COMMON across multiple OSes...