Oups, I hadn't seen the Ismael answer, sorry for the spam.
It's far from being finished (and I don't know if I will finish it), but Dan what do you think of that for your shirt :
That's a nice, simple design, but something's missing.
Oddly, the original drunken penguin shirts, or ripoffs thereof, seem to still be available at http://www.ixsoft.de/software/products/CWTSHIRTDP-L.html
Original artwork is at ftp://wine.codeweavers.com/pub/wine/logos/
I would kind of like a shirt that had the penguin opening the bottle on the front (text: Support the Wine Project), and the drunken penguin on the back (text: I did my part, or something like that) but I'd have to think a bit more on the text.
Other old links:
Martin's design: http://cross-lfs.org/~mlankhorst/t-shirt.png
Ismael Barros put some effort into this before: http://www.winehq.org/pipermail/wine-devel/2008-December/070894.html but nobody could think up good text.
- Dan