Sorting to find unique entries

Hi, I'm fairly new to VBA and programming in general and I've been presented with a task that has thrown me for a loop. I know it's not really a hard task but for some reason I can't grasp how I should do it. My question involves lots of data that is going to be changing on a weekly basis lets say in column A I have data

A
A
A
A
A
A
A
B
B
B
B
B
C
C
C
C

and I want to sort through this data and only find the "unique" data entries. ie. I only want A, B, C so that I can use them in a combo box for drop down selection. Right now I have it so that the drop down box is showing all the A's, B's, C's, etc. I know this can be done with some sort of sorting algorithm but I'm severely confused. Could anyone help me out?

You can use a second column to collect the unique values, then use that second column for your drop down.

Assuming column A has the original values, put this array formula in B1:

=INDEX(A$1:A$100,MATCH(0,COUNTIF(A$1:A$100,"<"&A$1:A$100),0))

...confirm by pressing CTRL-SHIFT-ENTER to activate the array. The first value should appear.

Then in B2, put this different array formula, also with ctrl-shift-enter:

=IF(COUNTIF(A$1:A$100,">" & B1), INDEX(A$1:A$100, MATCH(COUNTIF(A$1:A$100,"<=" & B1), COUNTIF(A$1:A$100,"<"&A$1:A$100),0)),"")

...and then copy that cell down as far as needed to get the rest of the values to appear.

Then use this column for your drop down.

CAVEATS:

Your data does not have to be sorted as you showed in your example, you'll still get an alphabetical listing.
Your data can't have any blanks in the range anywhere.

A macro approach to get sheet1 uniques to sheet2:

Sub CopyUniques()
    Sheets("Sheet2").Columns(1).Clear
    Sheets("Sheet1").Range("A:A").AdvancedFilter Action:=xlFilterCopy, _
        CopyToRange:=Range("AA1"), Unique:=True
    Range("AA2", Range("AA" & Rows.Count).End(xlUp)).Copy Sheets("Sheet2").Range("A1")
    Sheets("Sheet1").Columns(27).Clear
End Sub