Mac OS X Hints: Create Keynote slides from a series of images: "Here's a quick way to convert any number of images into new slides in Keynote.
Macworld - http://www.macworld.com/
If you’ve got a number of images that you’d like to convert into individual Keynote slides, it’s amazingly easy to do. In Keynote, make sure you’re in either Navigator or Light Table view (using the View menu); this trick won’t work in Outline or Slide Only view.
Switch to the Finder, and select all the images you’d like to use to create your slides. If Keynote is in Navigator view, drag the selection into the Slides column; if you’re using Light Table view, just drag the selection onto the light table area. Keynote will then import your images—you may see a progress dialog, depending on the quantity and size of the selected images—and place each one into its own slide.
By default, the images will be placed in front of any fields (title, subtitle, bullets) on the slides, so you’ll need to select each image and send it to the back to use the fields. Alternatively, you can force the images to be created on slides with blank masters. To do that, create a new slide, set its master to blank, and then drag in your source images.
Not a huge hint, but if you’ve ever labored with importing images, or dragging them into already-created slides one-by-one, this method is a great timesaver.