digiKam is a great software to manage your digital photographs. I like it especially because it does not depend that much on a database / proprietary ways to store information about the photos as it saves most information directly to the files.
sudo aptitude install digikam digikam-doc
To install it on Mac OS X using the Macports system as found here:
sudo port install digikam
- tips (German): http://www.gerhard.fr/DAM/deutsch.html
- moving from iPhoto to digiKam: http://sites.google.com/site/laurentbovet/photokam