Of course, there are a bunch that still rely on HTML links with remotely hosted images.
Near as I can tell, nowhere on the internet is there any type of script that can randomize a mix of both of these types of ads. It'd be a nifty widget, and one I can't imagine would be too difficult to write for someone who has some idea what they are doing. I have no idea what I am doing.
Bonus points if you can include a way to weight the frequency of the ads.