Shamelessly copied from VL, but a guy has hacked an original gameboy to display to a vector oscilloscope display. Very cool and an interesting write-up of how he does it. Might make for some interesting vector homebrew.
http://flashingleds.wordpress.com/2011/02/13/nintendoscope/
http://flashingleds.wordpress.com/2011/02/13/nintendoscope/