De Duping the database

Does anyone know of a plugin or a way to de dupe your database?

What I want to do is have a “primary record” on the left of the screen and when there is a potential duplicate in the database it will show on the right of the screen. I can then select one of the entries on the duplicate record and push it over to the primary record (assuming the primary needs updating). Then I would delete the dupe record with a click of the button after I’ve mined it for updated data.

Sounds like a great plugin. Anyone aware?