Just a place to track tricks and tips I’ve used.

Just used 2 handy ones(Excel 2003):

To identify a unique list of values from a column Choose Data->Filter->Advanced Filter
In the list range, choose the cells to check.
Click the “unique records only” box.
If you want to copy the unique list somewhere, choose “copy to another location” and select that location.

To look for intersection between two columns:
=IF(ISNA(MATCH(D2,E:E,0)),””,”X”)
D2 is the first cell to check. E:E means we are looking for dups in column E.
an X will show up if D2 is found in column E.
Copy the formula down as far as you want to check column D.