To create an iPhoto-like size-adjustable icon view of a folder, just put "" (with nothing inside the quotes) in the search box in a Finder window. Set it to the folder of interest, and to search by name, and choose icon view.
Now you can see a view with the zoom scroller on the bottom right. Very useful to see images or videos on folders.
[robg adds: This is a variation on this older hint, which used a smart folder to display a narrow range of results with the slider; this method just opens it up to all files within a folder. Alternatively, as noted in the original hint, you could just opt to leave the View Options window open instead, as it contains a slider for icon size (as well as grid spacing).]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090219044402544