wp_upload_mimes

/*
----------------------------------------------------------

    Plugin Name:    Extended Mime Types
    Plugin URI: http://blog.tahlequah.k12.ok.us/maxwellja
    Description:    Extends the allowed uploadable MIME types to include a WIDE range of file types. Created specifically for WPMS to allow a wider range of file types network-wide.
    Version:    1.0

    Author:     Josh Maxwell (Tahlequah Schools)
    Author URI: http://blog.tahlequah.k12.ok.us/maxwellja

----------------------------------------------------------
*/

// Add the filter
add_filter('upload_mimes', 'tqps_extended_mime_types');

// Function to add mime types
function tqps_extended_mime_types ( $mime_types=array() ) {

    // add your extension & app info to mime-types.txt in this format
    //   doc,doct application/msword
    //   pdf application/pdf
    // etc...
    $file = '/extended-mime-types/mime-types.txt';
    $file = plugins_url() . $file;
    $mime_file_lines = file($file);

    foreach ($mime_file_lines as $line) {
        //Catch all sorts of line endings - CR/CRLF/LF
        $mime_type = explode(" ",rtrim(rtrim($line,"\n"),"\r"));
        $mime_types[$mime_type[0]] = $mime_type[1];
    }

    // add as many as you like
    return $mime_types;
}