The good folks over at Spark Fun Electronics have a great input device that is a mate for their popular PSP 24-bit color LCD. This 4.3-inch 4-wire resistive analog touch screen is even prepped with adhesive for direct attachment to the PSP LCD. Be forewarned, you will have to develop (or locate) software for enabling a user interface with this screen add-on. The touch screen retails for $23.95, while the PSP LCD sells for $69.95. Now, if only these products had been available when I wrote, PSP Hacks, Mods, and Expansions (McGraw-Hill, 2006), then I might've sold more copies. Nah!
(Image: Spark Fun Electronics)