First of all, thanks for making this so easy to use with Joomla! I'm a bit of an optimization freak, and this is great! The debug feature is particularly helpful.

A great feature to add would be the ability to add a far future expires header to template graphics. Unlike regular graphics, they really only need to be loaded the first time and after any changes, so when they get loaded on every page load it's just a waste of bandwidth and time. Two different ways of doing that would be to either 1) add the expires header to all images accessed in the Joomla template folder, or 2) to just add them to images files for the active template.

Btw, one issue I noticed in testing my site at site-perf.com is that when bandwidth is unlimited, Speedy can actually slow down a website slightly. It seems that the optimized, cached JS and CSS files load more slowly than when they are unoptimized. I'm not sure if it is just the overhead caused by optimizing everything (though you'd think that difference would disappear after the files have been cached once), or some performance issue with the plugin that can be tweaked. Even though the slowdown is pretty consistent it's always less than 0.5 of a second for me, and obviously the benefits outweigh the slowdown the more limited the bandwidth.