Have been experimenting with LCD lights and the like without much luck so far but bought a few digital photo frames off ebay for a couple of pounds to use as advertising hoardings. I will try and incorporate these into the walls so they don't stand out too much and they do look pretty good first hand - you can have the pictures change every second or so. Photos don't do them justice.

Sample of the pictures I've uploaded (apologies bad flash from the camera)