Formula to count unique number of records in a column

I want to be able to count the total number of unique records for my analysis.

However.... I cannot do this by simply highlighting the column and seeing what the cell count is because there are duplicates in my data.

column A has a list of id's eg below: There are 5 unique records not 10.

I want to be able to get this unique record count for my long list of data.

123
123
123
456
456
750
100
236
236
236

Is there a simple formula I can use for this???

Many thanks in advance.

I found the answer I was looking for here----thanks anyway

=COUNTA($A:$A)-1

http://office.microsoft.com/en-us/ex...448621033.aspx