If you’re into JSFL you’ll no doubt know about “Extending Flash MX 2004” by Keith Peters and Todd Yard which is essentially the bible on Flash extensibility (though I have to admit there is little competition).
After reading Keith is letting the accompanying domain FlashExtensibility.com go, I got in touch and he graciously transferred the domain to me. Pretty cool, looking forward to building it up to a nice little resource on extending the Flash IDE!