Keyword Assistant is an iPhoto plugin that makes keyword management quicker and easier.
It adds a panel with an auto-completing text field for entering keywords. This makes it realistic to keep and assign large numbers of keywords, for example one for every person in a photograph. That's a good thing because it makes searching for a photograph pretty easy. Other niceties include the ability to alphabetize the Keywords list.
Keyword Assistant is currently localized for English, Danish, Dutch, French, German, Italian, Spanish, Swedish and Russian.