It should be clear by now that I love Leopard's Quick Look, particularly because of the modular way that Apple designed it so that it can be expanded and extended by third parties. And those third parties are responding! To keep track of all these plugins two interesting new sites have sprung up, QuickLook Plugins List and QLPlugins.
Each site has some good stuff not on the other so it's worth keeping an eye on both. Highlights include a neat trick for expanding video format support to mkv (Matroska video) files (and in principle others) and a plugin for Flash FLV files. (Both of these require Perian.)
In the years to come I suspect we're going to look back and wonder how we ever got along without Quick Look.
Thanks to everyone who sent these in!