iPhoto plug-in to add bulk keywords and manage keywords for thousands of photos. The best feature is Quick Assigner which adds keywords to many photos at same time. Kate’s detailed review.
Whether you have 300 or 10,000 photos in your iPhoto library, organizing the photos with keywords will help you quickly find what you are looking for.
9WR: Keyword Manager: Inserts, manages iPhoto keywords; simplifies nesting, tagging, adding keywords.