With many thanks to Jürgen Köller of mathematische-basteleien, we now have an excellent I Love Math shirt on Neatorama's online store. (The equation is from Gabriel Taubin).
I Heart (Curve) Math t-shirt, currently on sale for just $9.95: http://shop.neatorama.com/product-info.php?i-heart-curve-math-tshirt-pid102.html
More I Love Science shirts:
I Heart Biology - $9.95
I Heart Chemistry - $9.95
I Heart Physics - $9.95