Many of you will already know Unshelved. Always funny, often hilarious and sometimes just weird. And they do nice t-shirts too!
Also always good value, the Warrior Librarian. The book is pretty funny too.
And why not try Rex Libris. Damn hard for me to get hold of, even with two fine comic shops near to home; worth the effort mind. I cannot comment on the quality of the apparel, but the comic is good.