If you're looking for a way to create graphical colour displays with your Arduino, but need something much larger - then Arduino forum member carl47's approach may be of interest. They have created a way of using an inexpensive Android tablet as an output device for an Arduino, and is clever in its simplicity.
A supplied program runs on the Android tablet, which accepts serial commands from the Arduino via USB - and by using an OTG cable can also power the board. Then the required graphics are requested by the Arduino using the special library - with an example of the output shown below:
Apart from being a fully Arduino Uno-compatible, it has onboard microSD socket and the full USB socket and host-mode controller. As well as the Bluetooth application described above, this is the ideal platform for developing peripherals or projects based around Android devices with ADK (Android Developer Kit) functionality, but without requiring a USB host controller shield stacked onto an Arduino. For more information and to order, visit the product page here.