Raspberry Pi is a powerful but small Linux based computer board that gained its popularity in the hobby world. It has everything you need to build a computer except display. Since there are no DSI based display modules available, people try to solve this problem in several ways. They use HDMI based displays, composite video, serial monitors. Probably most of small projects rely on GPIO where they plug in their custom boards with various types of LCDs. This seems to be OK, but running such displays usually require additional driver/software to run and it occupies I/O pins, that can be used for other purposes. While we are waiting for official Raspberry Pi DSI display we have to deal with those workarounds.
The choice is really big. You can find may types and sizes of displays driven through GPIO. Percheron Electronics Ltd are running kickstarter campaign where they offer to give a shot with their offered e-ink display solution. It comes on a module board that plugs in to Pi’s GPIO. Display resolution is 264×176. The main advantage of using such display that it practically requires no power supply when displaying statical information. It only draws a bit when changing its contents. Display module comes with RTC clock built in which can be used by Raspberry Pi to track time precisely or work as a clock for display itself. E-INK display is great choice if you plan on building battery powered project where you need to represent information as text or graph. They are not meant for high FPS, but for text information like clock, weather, social feeds or basic B/W graphics it is great.