While searching for a decent open-source Inversion of Control / Dependency Injection framework that works w/o having to declare code in XML (ie, JICE), or implement special interfaces (ie, Fortress), I came across PeaPod, which, from a cursory glance, looks like it may begin to answer the plug-in pattern someone was looking for within the last week.
http://www.peapod.org/If you know of any IoC frameworks worth using (Spring seems to answer this, but I don't want to have to deploy the entire Spring jar, nor rip out pieces and parts), please pass on any relevant info.. else, I'll be coding one today. I've done one before, based on .properties files, modeled aftert ATG's configuration framework.. But, i don't have my code with me on-site, nor do I feel like going through the hassle of licensing it to a state entity.