I frames are starting to make some interesting site designs possible. The other day we came accross this one which uses a combination of iframes and javascript: Cantalope Music.
Click on a link in the left iframe and it will load content in the right iframe and show a different image to the left.
When we get a few minutes we should really whip up a simpler demo of the concept of using iframes. We have many handy tricks we use them for as well (for example includes without shtml or php). They are now accepted in all major browsers contrary to common belief.
One problem with this site is that it is very slow to load because the images and iframe content is apparently preloading.
The source for this page is a tad difficult to decipher because of it’s complexity, but the idea is pretty good.