The first code comes from the GIA's own J.T. Kauffman; it is apparently circulating Japanese message boards and web sites. The code is: hold down L1, Circle, and Select. This code has worked with both the Dual Shock 1 and 2 with about 40% accuracy.
The second code comes from a friend of the GIA known as Barubary. The code is: press in L3 (the left analog stick) straight and hard. This code does not work with the Dual Shock 1, but works with the Dual Shock 2 with about 60% accuracy.