I read bunches of excel tips and hints from other websites and every now and again I post links and details of the best ones. Here's a few good ones I have picked up recently.
Counting number of unique entries in a specified range From ExcelTip
Counting number of unique entries in a specified range is simple by using the SUMPRODUCT and COUNT functions.
The range can be all in one column or row, or may span multiple (adjoining) columns/rows.
The formula would be written as: =SUMPRODUCT((1/COUNTIF(A1:C5,A1:C5&""))) where A1:C5 is replaced with the range you want to apply the count to.