Dang, I should have known that all this time I've been silently complaining about not being able to view some kinds of multimedia on the web in Linux, a solution was sitting right under my nose. MPlayer has codecs for AVI, WMA, RealPlayer and Quicktime, among many others. It'll even play DVDs and Video CDs. MPlayer Plug-in handles all those embedded media files flawlessly. Both projects provide binary RPMs for i386 Linux, which means easy download and install for everything. I'm using a non-RPM install for Mozilla, of course, which meant I had to symlink the plug-in into its proper place, but otherwise everything just worked!
I can't believe it! I'm watching Quicktime movie trailers directly off Apple's web site, and I'm not using any commercial software to do it! :)