There is lots of interest in Ubuntu t-shirt designs. Here are some links and info.
Canonical's store with tshirts et al.
Land's End shirts etc: http://ubuntuforums.org/showthread.php?t=529667
LoCoTeams/GroupBuy - how to organize loco teams to order merchandise
Simira's Ubuntu T-shirts
Simira is out of t-shirts and closed the business!