Awhile back I was playing with a CS4954 Video Encoder. It's a great little chip, inexpensive, supports NTSC/PAL, S-Video, SCART, etc via 6 on board 10-bit DACs.
Here is my NTSC/PAL breakout board:
It runs off 5V or 3.3v and requires a 27MHz clock. The interface is via 8bit parallel bus or I2C. If you use I2C, the 8 bit parallel I/O bus becomes an 8 bit GPIO! The pixel data is fed to it via a dedicated 8 bit bus. Using I2C you basically get these I/O lines back with the GPIO.
It supports both Master mode where it will supply the vertical and horizontal syncs or Slave where those signals are provided by the host device.
I have seen some cool things done with this chip in the 6502.org forums with FPGAs and was curious if anyone would like to help me get some VHDL going on Papilio for this thing. I have the i2c start up sequences to get output running and have drawn some simple patterns with it using an Arduino, but that's about it.