As you can probably tell, I think graphic compression is also low-hanging fruit. It's a rare gif file that needs 256 colors (on small images, 16 is amazing); it's a rare online jpg that needs more than 40% for compression; and only png files that truly need an alpha channel should be saved at 24-bit.
I'm amazed at how graphics are abused online. The Photoshop option says "save for the web" - which, by the way, also removes some of the embedded xml data and that trims the file even further - so remember the "web" part.
Has anyone got any other low-hanging fruit for improving site speed?