I read an article Merging Lists To A List Of Distinct Values at CPearson. The article describes code that you can use to merge two lists into a third list and prevent duplicate entries in the resulting list,  using VBA to create a macro.

Here is a solution to create a unique list from two columns without using VBA.

The picture below shows the unique list and the unique distinct list.

Named ranges
List1 (A2:A5)
List2 (C2:C6)

Unique values

Here is the  array formula in A10:

=IF(ROWS(A9:\$A\$9)<=SUM(IF(COUNTIF(List1, List1)+COUNTIF(List2, List1)=1, 1, 0)), INDEX(List1, MATCH(0, IF((COUNTIF(List1, List1)+COUNTIF(List2, List1))*NOT(COUNTIF(A9:\$A\$9, List1))=1, 0, COUNTIF(List1, List1)+COUNTIF(List1, List2)), 0)), INDEX(List2, MATCH(0, IF((COUNTIF(List2, List2)+COUNTIF(List1, List2))*NOT(COUNTIF(A9:\$A\$9, List2))=1, 0, COUNTIF(List2, List2)+COUNTIF(List1, List2)), 0)))

Unique distinct values

Here is the array formula in C10:

=IF(ROWS(C9:\$C\$9)<=SUM(1/COUNTIF(List1, List1)), INDEX(List1, MATCH(0, COUNTIF(C9:\$C\$9, List1), 0)), INDEX(List2, MATCH(0, COUNTIF(C9:\$C\$9, List2), 0)))

How to create an array formula

1. Select cell C10
2. Copy/Paste array formula
3. Press and hold Ctrl + Shift
4. Press Enter

How to copy array formula in cell C10

1. Select cell C10
2. Copy (Ctrl + c)
3. Selelct cell range C11:C15
4. Paste (Ctrl + v)

How to customize the formula to your excel workbook
Change the named ranges. If your unique list starts at F3, change C9:\$C\$9 (or A9:\$A\$9)  in the above formula to \$F\$2:F2.

Possible blanks in the two lists

Array formula in c10:

=IF(ROWS(C9:\$C\$9)<=SUM(IF(COUNTIF(List1, List1)=0, 0, 1/COUNTIF(List1, List1))), INDEX(List1, MATCH(0, IF(List1="", 1, COUNTIF(C9:\$C\$9, List1)), 0)), INDEX(List2, MATCH(0, IF(List2="", 1, COUNTIF(C9:\$C\$9, List2)), 0)))

unique-list-from-two-columns.xls
(Excel 97-2003 Workbook *.xls)

IF(logical_test;[value_if:true];[value_if_false])
Checks whether a condition is met, and returns one value if TRUE, and another value if FALSE

ROW(reference) returns the rownumber of a reference

ROWS(array) returns the number of rows in a reference or an array