Between Flash/Silverlight and native is Java. With Java7, you get GPU accelerated multimedia, "applets" not restricted to the browser, point & click deployment with Upstart ..

Very few people are doing client-side java these days, but those are making some rich, immersive experiences, across platforms, and with push deployment.

Having said that, client-side java is hard; No "authoring" tools, all UI & visualization is made by programmers .. not exactly the most discerning of aesthetes ;-)

I am possibly very biased about this. My opinion is that Silverlight is strictly superior to Java as a CLIENT-SIDE technology in terms of speed (runtime and startup time), memory, penetration (see http://riastats.com), supporting and tooling, language support, feature set (GPU, out-of-browser, etc), and deployment. If SL and Flash cannot survive, client-side Java browser plugin has no chance.

To be honest, when I got a technology budget a few months ago, I put my boss' money on Android and HTML4, not flash, silverlight or java applets. So ..