The LEGO Brick Construction Shirt from ThinkGeek is a $18 shirt with a LEGO baseplate fashioned to the chest. You can build whatever the hell you want on the front of that bitch. I'm gonna build a functional rocketship on mine!
Take your favorite construction blocks of choice (LEGOâ„¢, PixelBlocks, Mega Bloks, K'NEX Bricksâ„¢ are all compatible) then start building. You can write messages, incorporate minifigs, build 3-D structures with gears, add motors... the mind boggles. The only limit is your imagination and the amount of weight you can deal with on the front of your shirt.
I figure I'm good for a solid 40lbs of weight on the front of my chest. And not just cause I carried a baby raptor full-term, but I totally did. Sucker burst out of my chest like an alien and ate the cat! I swear, what a little rascal.