[homofaber]

If you have only few minutes before execution, and want to fix an old X programming mystery, I would suggest dwm.c: http://hg.suckless.org/dwm/file/e901e70f69e8/dwm.c

It is so easy to understand inner workings of window manager in X reading this code, and you do not need much time for it (>2000 SLOC).

[IvarTJ]

As a relatively new C programmer, I have followed the dwm source code while trying to make my own window manager. It has been very helpful.