I hope to add from time to time new plugins that I use myself.
As mirrorless cameras become more common, people use these cameras with legacy lenses, but the lenses info are not always stored in the EXIF info of the photograph. I also still scan film images, and these of course also do not have EXIF info.
Lenstagger http://www.essl.de/wp/software/lenstagger-lightroom-plugin/ is a Lightroom plugin that you can use to set this information in the raw file directly from Lightroom. A tool that I use for scanned images is AnalogExif, http://sourceforge.net/projects/analogexif/ which is a bit faster to apply on bulk images before adding them in Lightroom.