On my own time, I've done some stuff.
A port of xscreensaver-3.22 by JWZ.
Download: Win32 screensaver
It's probably pretty broken. I haven't touched it for a couple of years.
It uses OpenGL though.
Source code notes: notes.txt
I also ported XSoldier to Win32.
The original one is here: XSoldier
I also made a port of X11R6.4 server to Win32 because the ones out there either cost money or are too old.
I ported netris to windows for nic.
I like to port things to windows. I'm not saying that windows is better than any other GUI, but it's just fun and easy to do.