In a former article I mentioned that I had begun using a new login manager for my laptop computer - running FreeBSD. Well, this login manager is - as its name implies - very simple. All it has is a wallpaper, an overlay image (PNG) with transparency and some parameters on where to show the login prompts. It really is simple; but far more interesting to the eye than xdm ... and a less steep learning curve.
SLiM has the ability to randomly select a theme among several.