Resizing an iframe based on content

I am working on an iGoogle-like application. Content from other applications (on other domains) is shown using iframes.

How do I resize the iframes to fit the height of the iframes' content?

I've tried to decipher the javascript Google uses but it's obfuscated, and searching the web has been fruitless so far.

Update: Please note that content is loaded from other domains, so the same-origin policy applies.

Source: Tips4all