There are several choices out there, but the big two guns in the industry are Aperture, Apple’s professional photography application, and Photoshop Lightroom 3 from Adobe.
I use Aperture myself, and several of the big differences with iPhoto are that Aperture lets you make many changes to an image but still backup to the master file very easily. And Aperture keeps each image in its own file, rather than one file for all photos, like iPhoto, which is problematic as iPhoto’s library can grown very large and slow.
Aperture will easily import your iPhoto library: go to File/Import and select iPhoto library. And there’s lots of help online at Apple – Support – Discussions – Aperture.
It might come down to what’s called workflow and how you work and how that fits into the ways Aperture or Photoshop Lightroom help you work. Each is designed to be efficient when it comes to transferring photos from your camera, organizing them, filing them and making backups.
And to make the best of either program, you might want to check and see if your camera exports in RAW format, and if it does, check to see if your camera is supported by either Aperture (Aperture RAW Support) or Lightroom (Lightroom Camera Raw).
The best thing to do is try a demo of each. You can get a 30 day demo of each and try it out, and at the end of the trial period either buy one or delete it. Or stay with iPhoto for now.