Note: I'm listing the products in alphabetical order (sorry, Bacula).
I especially like this quote from the last link:
Whether you choose Amanda or Bacula will depend greatly on your individual network setup. If you have a single server with a tape drive that you use to backup all the rest of your systems I would suggest Amanda. On the other hand, if you have multiple servers, each with there own tape drives, and a limited backup window, I would suggest Bacula. For those familiar with the commercial backup products, you might compare Amanda to Retrospect and Bacula to Veritas Backup Exec, to clarify things in your mind.
I like this list as a starting point for specifying one's needs: