I am currently using the Plug in Background Manager (http://wordpress.org/plugins/background-manager). You can set the background to change on page reload, every 10s-hours and it has awesome transition features.
I'm trying to find a plug in JUST like this, but for logos/banners for the top page (which will show up on every page, like a logo). For each time the background changes, I want a new logo as well. Having it set up this way, it'd be like interchangeable layouts!