OK, this one is a stand-alone app not a plug-in, but it is an incredibly useful tool for iPhoto users.
Normally, you only have one iPhoto library for all of your photos. You then navigate that library through albums, events, and keywords. This single-library system can slow down iPhoto and get a little messy when you have thousands of photos from years of parties, birthdays, and trips. iPhoto Buddy’s solution is to create multiple libraries and manage them outside of iPhoto. You can create a new iPhoto library and see details about existing libraries—all without opening iPhoto. Double-click on a library within iPhoto Buddy to open it up in iPhoto.
iPhoto Buddy; Free