I stumbled upon a good tiny widget which allows to “rotate” chunks of HTML code in your sidebar (using wordpress widgets plugin).
You may set up a couple of this rotators for different content types (e.g., text links, banners, google ads), and within each block put a number of alternatives, separated with a standard < --!more-- > tag (with no spaces, of course). Now each time when your page is shown, each instance of AdRotator will show one of the alternatives you put into it. Pretty simple and useful!
