To help you find particular images, iPhoto can sort your pictures based on the following criteria:
Date
Keyword
Title
Rating
To sort pictures, make sure you tagged your pictures with keywords, titles, or ratings and then do the following:
In iPhoto's left pane, click Events or Photos, or click the album that contains the pictures you want to sort.
Select View ▸ Sort Photos and choose By Date, By Keyword, By Title, or By Rating. The iPhoto program sorts your pictures.
(Optional) Select View ▸ Sort Photos and choose either Ascending or Descending.