Contact Clearout is an application that straightens out your contacts and cleans up data issues. The program helps you not only remove duplicates, but also allows you to find those cards that are not identical but are for the same person.
If you put someone's phone number into your phone but later you made a separate entry on your iPad with the e-mail and home address, Clearout will scour your database and show you both entries, so you can combine them in a complete and seamless workflow.