Thanks to Tim Jackson for bringing this one to my attention. Since I've worked in Coldfusion I've always used code similar to this:

So that I could avoid the "This page contains unsecure items." message when embedding Flash, Javascript, images, etc.

Tim advised me that he had found a new way to avoid this without using server-side code:

Apparently the browser retains the current protocol. I've tested this in IE7 and Firefox using images, Flash, anchors, and javascript.