Ynvisible (based in Portugal) is developing flexible transparent electrochromic e-paper like displays, Electrochromic materials change their color when electricity is applied. The company is already producing some displays in low volume (and offering some "demo" devices on-line), and were kind enough to send our sister site E-Ink-Info a sample gift card showing off their displays.
The display is quite impressive. It's very basic (it shows a pre-printed image and has a very low contrast), but it's transparent, and flexible and frankly very nice. The material they use in this sample changes from transparent to being blue. When off, it looks exactly like a normal piece of plastic - totally transparent and bendable (flexible).