FindBugs is uses static analysis to find potential bugs in Java code.  It is free software, distributed under the terms of the Lesser GNU Public License. Since CafePress won't let me have more than one design for each shirt, I've selected comparable shirts for some alternative designs.

Marmoset Project Swag for the Marmoset project	FindBugs 1.1 Null Pointer Bugs $21.99	Univ. of Maryland Computer Science $18.99
FindBugs Black T-Shirt $21.00	FindBugs 2.25" Button (100 pack) $99.99	FindBugs Organic Cotton Tee $21.00
FindBugs Null pointer Ash Grey T-Shirt $19.00	FindBugs Ignored Return Values T-Shirt $19.00	FindBugs Infinite loop Fitted T-Shirt $21.00
FindBugs Infinite Loop Ringer T $19.00	FindBugs T-shirt $10.00	FindBugs 2.25" Magnet (10 pack) $13.99
FindBugs Infinite Loop Golf Shirt $22.00	Mug $11.00	Mousepad $11.00
Tote Bag $13.00	FindBugs Round Ornament $6.00	FindBugs Keepsake Box $20.00
FindBugs Button (10 pk) $13.99