Further encouraging active participation, code4lib 2006 is currently having a t-shirt design contest. The winner gets to see their design on the official code4lib 2006 t-shirt, given to every attendee of the conference.
If you are interested in submitting a design, you may use the following template (graciously borrowed from cafepress.com): http://www.cafepress.com/content/si/temp_10x10_apparel.zip. Submitted designs will be added to this post, and we will hold a public vote on the designs next week.
The only major restriction to be aware of is that at this time, we are unsure if the t-shirts will be full-color or 1 color. So, while your design may be in color, it should also work as a 1-color design as well (you may submit two versions of a design to meet the above criteria).