Lightroom is very extensible, and there are a lot of plug-in authors out there. In the book I show several which are part of my regular toolkit.
Search Replace Transfer by my fried John Beardsworth is useful for manipulating metadata in a nearly infinite number of ways. In the book I show how it can be used to auto-populate the IPTC Location fields from a set of keywords (and also the reverse). Available for about $25 from Photographers Toolbox.
LR/Transporter by Tim Armes can match data in a CSV document to image files. This can be very useful when you have information about the images in a database or spreadsheet. Available for the donation of your choice to Photographer’s Toolbox.
SmugMug Publish Plugin This allows you to send images up to SmugMug and still control them from the Lightroom catalog. It’s a great way to share with friends and family.
Libris Plugin – Business and institutions that need to make an archive available to a controlled group of people can use Librisfor robust controlled distribution. As of this writing (6/17) the plugin is nearly finished a new update. Note that readers can get a 10% discount on Libris by signing up for a demo here. The referral code is DAM.