Two weights of T-shirts, plus a golf shirt for the collarly-inclined, and two long-sleeved shirts (just in case DC is a bit chilly in March).
All prices are only US$1.00 over cost; proceeds will benefit the PSF.
Incidentally, a number of people have mentioned the Adminspotting shirts. I was aware of them, but I can't say that Adminspotting directly inspired Choose Python. I'd been wanting to rent Trainspotting when I got a chance, so it was at the front of my brain at the time.
UPDATE 2: Enough people have asked about permission to use, modify, etc. that I want to make it clear and official: I hereby release the text, rendering, and design of "Choose Python" to the public domain.