This is not exactly a quine, but is a neat quine-related curiosity:
int n=103;char*f="int n=%d;char*%c=%c%s%c;
This code (newlines removed) prints out an other C program, which in turn prints out the original code (I could've equally supplied this code's output).

This is not a bi-quine nor a multi-quine, I'm not sure what to call it.