For Excel 2007 and newer:
Select the data you want to extract unique values from, and under the Data tab, click on Remove Duplicates.
If the column you select is alongside other data, it will remove those cells as well. If that’s not what you want, I’d recommend copying the column over somewhere else so it is by itself, and then click on the Remove Duplicates button.
For Excel 2003 and older:
Run an Advanced Filter on the column that you want to extract duplicates from, leave the criteria Blank, select Copy to Another Location, and select Unique Records Only.
Note, select the advanced filter option when you are in the sheet you want to extract the values to. For example, if your data is on sheet 1 and you want to extract the duplicates to sheet 2, you need to select advanced filter while you are on sheet 2, otherwise there will be an error.