Chris made this excellent tutorial on creating a VGA test box with a PIC microcontroller. He writes:
For quite some time I’ve been wanting to create a device that outputs VGA signals. My main goal was of course to be able to display whatever I wanted on the monitor I was currently using. The goal of this project is to create a device that is capable of outputing VGA signals to a CRT monitor inorder to display figures, text and characters. This will be done using a Microchip PIC microcontroller at 4 MHz clock speed. The programming required to achieve the VGA timing signals must be done in low level assembly because of the high level of precision that is necessary. The hardware assembly is just basic buttons, switches & wire that you can purchase from local electronics stores.