Gmail finds and merges duplicate contacts. Brilliant.
Here's how:
1. Open up Gmail.
2. Click on the "Contacts" link in the left navigation.
3. Your "Contacts" frame will open.
4. To the right of the screen, you'll find a button that says "Find duplicates".
5. Click on "Find duplicates". Notice all duplicates listed.
6. Select/Unselect contacts of choice. Then click "Merge".
That's it! Another great addition from the Gmail team.
For more details, go to the Gmail blog here.