You can design your own at CafePress, at least in the US. I made a coffee mug that I really like... http://screencast.com/t/9sj4yyKBOh2 But you can search there for various stuff people have made: http://shop.cafepress.com/bioinformatics
I can imagine some fun designs with cool data.
I like zazzle, you can get Bioinformatics cartoons or DNA helix to be printed on T-Shirts, Mugs theirs or your own custom ones. I like printing a quote with a small fig or logo. Also, check this post to see some on the cartoons leaned towards Bioinformatics for inspirations.