So I'm actually working on several display solutions for the Spark Core right now.
There's so many different 16x2/20x2/20x4 LCD backpacks on the market, each with different command sets. I started out writing a library for the Parallax Serial 16x2 LCD Backpack, however it's turned into more of a Universal Liquid Crystal Library. It'll support all the same commands as the Arduino Liquid Crystal Library, but I'm structuring it so that you can use #define statements (or custom functions) to enter the commands your specific backpack expects. It'll support Serial and I2C backpacks.
I've got a port (well, really a re-write) of the Digole SPI/I2C/UART Library I'm working on now.Finally, I've got a primitives and UI library that should work with @Jamjardavies Color OLED and pretty much any other display, so long as you can hack together a basic driver for it. 