In a recent post to his blog Daniel Cousineau shows a method for correctly outputting CSV data in push down to the client browser as a method of export.

Nearly every application you could write in for the business sphere in PHP probably requires some sort of data export, most likely in the CSV format. The easiest way to provide a downloadable file is by altering the headers and echo'ing the file content.

His method sets the headers for the CSV file type then pushes the content out (contained in an array) via the fputcsv function. He wraps it all in a function near the end for simple cut and paste.