The chaps over at the Batsocks blog sell a cute little gadget called the "Tellymate": a nice little serial->video converter that is very, very simple. It uses a single Atmel AVR Mega, and handful of other extra components to implement a full character mapped 38x25 character display terminal which reads characters from a serial input port. But what's really great is that they have all sorts of good information on how the gadget actually works, meaning that you can adapt the techniques and ideas for your own use. Very cool.
The interesting bit that the Tellymate implements is a higher density display than can be achieved with the arduino TV-out library that I mentioned a few days ago. It does this by leveraging the SPI output to automatically clock out bits 9 at a time, which gives you enough time to actually stream out 38 characters (about double what I can achieve with the Arduino library). Very neat, but there are some details which are a bit crufty. Lots of good information.