Here is a JPG http://www.flickr.com/photos/splat/49792783/in/set-981332/ at the main link.
Well, it's a picture of a whole site.
Here is a Gig http://www.cwsomaha.com/templates/cwsomaha.com/images/widget.gif
It's from site http://www.cwsomaha.com/
This site has some nice ones.
I couldn't find a png at the sites you mentioned but i did find one at Apple.
It seems that 99% of the images are jpgs