I know I rave on and on about it, but the TVout lib is a nice easy bang for the buck, especially since there's a lot of bang but absoltely no bucks. Two resistors and you can generate video off the thing, which makes for a nice easy, but fun project.
The code would be very simple also, you could write something that displays some text, some graphics, maybe some analog input.. whatever.. but because the circuit is so simple, it makes for a quick success (which breeds interest in more complex things) for most people starting out who want to "see something come out of it".