Do the lists contain the same fields (ie first name, last name ..etc)

If you have Excel you can use conditional formatting to highlight the duplicates (Conditional Formatting -> New Rule -> Format only unique or duplicate values -> Select a formatting style). If you format it as a table and then sort by one of the columns then you should see all of the duplicates listed together and you can remove the duplicate rows manually.

Edit: The Robert/Bob thing does cause an issue with this method, but I think it's still a viable option.