This morning I was perusing the links for light reading sent by Russ from the WSG when I came across this article: Insert HTML page into another HTML page, where the author had discovered a way to use the object element instead of iframes to display third party content within a page.
The main issue he had was getting IE to work with this method but ingeniously he solved this problem by working out the classid reference needed to use IE as a plugin to IE. This makes this solution work cross-browser.
In discussion this morning with my colleagues Brad and Mike. Brad went off and made a few optimisations by reducing the need to have separate object markup for IE and everything else as classid is a perfectly valid attribute. He also made a fix to the styling for IE so that the object renders correctly in HTML 4.01 strict too.
See Brad's test case here: http://intranation.com/test-cases/object-vs-iframe/
Looks like this could be a viable technique that could be used to replace the use of iframes for loading in 3rd party content.