A new feature in Flash Player 11 and Adobe AIR 3 is the feature to use JPEG XR. A enhanced JPEG format.
But how to generate or convert JPEG XR files. I found no Photoshop Plugin. All open source tools aren’t able because of licensing problems. The only tool i found is XN View, which can convert PNG files including the alpha channel to JPEG XR.
But you have to use the „Batch Convert“ tool. Only there is the option to convert to JPEG XR.
After converting you can load and use the JPEG XR files via Actionscript. e.g. with a Loader or via embedding. It behaves like a PNG file but with much smaller size while keeping very good quality.