Picasa 3.5 with Name Tagging

Works really well at automatically grouping pictures of the same person together.  Download Picasa

Picasa Basics: New features in Picasa 3.5

Picasa 3.5 now has name tags, based on the same technology that powers name tags on Picasa Web Albums. With name tags, you can organize your photos based on what matters most: the people in them. In this new version, you can also more easily geotag photos using Google Maps, plus import photos from your camera and upload them to Picasa Web Albums in one step. Get started by downloading Picasa 3.5 for PC or Mac at picasa.google.com

People

Add name tags - Picasa 3.5 scans all the photos in your collection, identifies the ones with faces, and groups photos with similar faces together. It's easy to add name tags to dozens of photos at once by clicking "Add a name" below a photo and typing the person's name. Once you've tagged some pictures, you can make a face collage with one click, easily find all your pictures with the same two people in them, or upload your name tags to Picasa Web Albums. Learn more.

Read more about Picasa 3.5 here: http://googlephotos.blogspot.com/2009/09/announcing-picasa-35-now-with-name-tags.html