Simple code useful if you don't want a WordPress plugin to show an update notice.

no_update_plugin.php

<?php
/**
 * Keep your plugin from updating
 * http://markjaquith.wordpress.com/2009/12/14/excluding-your-plugin-or-theme-from-update-checks/
 */
function s25_plugin_no_update( $r, $url ) {
    if ( 0 !== strpos( $url, 'http://api.wordpress.org/plugins/update-check' ) )
        return $r; // Not a plugin update request. Bail immediately.
    $plugins = unserialize( $r['body']['plugins'] );
    unset( $plugins->plugins[ plugin_basename( __FILE__ ) ] );
    unset( $plugins->active[ array_search( plugin_basename( __FILE__ ), $plugins->active ) ] );
    $r['body']['plugins'] = serialize( $plugins );
    return $r;
}
 
add_filter( 'http_request_args', 's25_plugin_no_update', 5, 2 );