Original DBT Code

<?php

/**
 * Create meta boxes for editing pages in WordPress
 * Compatible with custom post types in WordPress 3.0
 *
 * Support input types: text, textarea, checkbox, radio box, select, file, image
 *
 * @author: Rilwis
 * @url: http://www.deluxeblogtips.com/2010/04/how-to-create-meta-box-wordpress-post.html
 * @version: 2.2
 *
 * Changelog:
 * - 2.2: add enctype to post form (fix upload bug), thanks to http://www.hashbangcode.com/blog/add-enctype-wordpress-post-and-page-forms-471.html
 * - 2.1: add file upload, image upload support
 * - 2.0: oop code, support multiple post types, multiple meta boxes
 * - 1.0: procedural code
 */

/******************************

Edit meta box settings here

******************************/

$prefix = 'dbt_';

$meta_boxes = array();

// first meta box
$meta_boxes[] = array(
    'id' => 'my-meta-box-1',
    'title' => 'Custom meta box 1',
    'pages' => array('post', 'page', 'link'), // multiple post types
    'context' => 'normal',
    'priority' => 'high',
    'fields' => array(
        array(
            'name' => 'Text box',
            'desc' => 'Enter something here',
            'id' => $prefix . 'text',
            'type' => 'text', // text box
            'std' => 'Default value 1'
        ),
        array(
            'name' => 'Textarea',
            'desc' => 'Enter big text here',
            'id' => $prefix . 'textarea',
            'type' => 'textarea', // text area
            'std' => 'Default value 2'
        ),
        array(
            'name' => 'Select box',
            'id' => $prefix . 'select',
            'type' => 'select', // select box
            'options' => array('Option 1', 'Option 2', 'Option 3') // array of options for select box
        ),
        array(
            'name' => 'Radio',
            'id' => $prefix . 'radio',
            'type' => 'radio', // radio box
            'options' => array( // array of name, value pairs for radio options
                array('name' => 'Name 1', 'value' => 'Value 1'),
                array('name' => 'Name 2', 'value' => 'Value 2')
            )
        ),
        array(
            'name' => 'Checkbox', // check box
            'id' => $prefix . 'checkbox',
            'type' => 'checkbox'
        )
    )
);

// second meta box
$meta_boxes[] = array(
    'id' => 'my-meta-box-1',
    'title' => 'Custom meta box 1',
    'pages' => array('post', 'film', 'album'), // custom post types, since WordPress 3.0
    'context' => 'normal',
    'priority' => 'high',
    'fields' => array(
        array(
            'name' => 'File upload',
            'desc' => 'For file upload',
            'id' => $prefix . 'file',
            'type' => 'file' // file upload
        ),
        array(
            'name' => 'Image upload',
            'desc' => 'For image upload',
            'id' => $prefix . 'image',
            'type' => 'image' // image upload
        ),

    )
);

/*********************************

You should not edit the code below

*********************************/

foreach ($meta_boxes as $meta_box) {
    $my_box = new My_meta_box($meta_box);
}

class My_meta_box {

    protected $_meta_box;

    // create meta box based on given data
    function __construct($meta_box) {
        if (!is_admin()) return;

        $this->_meta_box = $meta_box;

        // fix upload bug: http://www.hashbangcode.com/blog/add-enctype-wordpress-post-and-page-forms-471.html
        $current_page = substr(strrchr($_SERVER['PHP_SELF'], '/'), 1, -4);
        if ($current_page == 'page' || $current_page == 'page-new' || $current_page == 'post' || $current_page == 'post-new') {
            add_action('admin_head', array(&$this, 'add_post_enctype'));
        }

        add_action('admin_menu', array(&$this, 'add'));

        add_action('save_post', array(&$this, 'save'));
    }

    function add_post_enctype() {
        echo '
        <script type="text/javascript">
        jQuery(document).ready(function(){
            jQuery("#post").attr("enctype", "multipart/form-data");
            jQuery("#post").attr("encoding", "multipart/form-data");
        });
        </script>';
    }

    /// Add meta box for multiple post types
    function add() {
        foreach ($this->_meta_box['pages'] as $page) {
            add_meta_box($this->_meta_box['id'], $this->_meta_box['title'], array(&$this, 'show'), $page, $this->_meta_box['context'], $this->_meta_box['priority']);
        }
    }

    // Callback function to show fields in meta box
    function show() {
        global $post;

        // Use nonce for verification
        echo '<input type="hidden" name="mytheme_meta_box_nonce" value="', wp_create_nonce(basename(__FILE__)), '" />';

        echo '<table class="form-table">';

        foreach ($this->_meta_box['fields'] as $field) {
            // get current post meta data
            $meta = get_post_meta($post->ID, $field['id'], true);

            echo '<tr>',
                    '<th style="width:20%"><label for="', $field['id'], '">', $field['name'], '</label></th>',
                    '<td>';
            switch ($field['type']) {
                case 'text':
                    echo '<input type="text" name="', $field['id'], '" id="', $field['id'], '" value="', $meta ? $meta : $field['std'], '" size="30" style="width:97%" />',
                        '<br />', $field['desc'];
                    break;
                case 'textarea':
                    echo '<textarea name="', $field['id'], '" id="', $field['id'], '" cols="60" rows="4" style="width:97%">', $meta ? $meta : $field['std'], '</textarea>',
                        '<br />', $field['desc'];
                    break;
                case 'select':
                    echo '<select name="', $field['id'], '" id="', $field['id'], '">';
                    foreach ($field['options'] as $option) {
                        echo '<option', $meta == $option ? ' selected="selected"' : '', '>', $option, '</option>';
                    }
                    echo '</select>';
                    break;
                case 'radio':
                    foreach ($field['options'] as $option) {
                        echo '<input type="radio" name="', $field['id'], '" value="', $option['value'], '"', $meta == $option['value'] ? ' checked="checked"' : '', ' />', $option['name'];
                    }
                    break;
                case 'checkbox':
                    echo '<input type="checkbox" name="', $field['id'], '" id="', $field['id'], '"', $meta ? ' checked="checked"' : '', ' />';
                    break;
                case 'file':
                    echo $meta ? "$meta<br />" : '', '<input type="file" name="', $field['id'], '" id="', $field['id'], '" />',
                        '<br />', $field['desc'];
                    break;
                case 'image':
                    echo $meta ? "<img src=\"$meta\" width=\"150\" height=\"150\" /><br />$meta<br />" : '', '<input type="file" name="', $field['id'], '" id="', $field['id'], '" />',
                        '<br />', $field['desc'];
                    break;
            }
            echo    '<td>',
                '</tr>';
        }

        echo '</table>';
    }

    // Save data from meta box
    function save($post_id) {
        // verify nonce
        if (!wp_verify_nonce($_POST['mytheme_meta_box_nonce'], basename(__FILE__))) {
            return $post_id;
        }

        // check autosave
        if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE) {
            return $post_id;
        }

        // check permissions
        if ('page' == $_POST['post_type']) {
            if (!current_user_can('edit_page', $post_id)) {
                return $post_id;
            }
        } elseif (!current_user_can('edit_post', $post_id)) {
            return $post_id;
        }

        foreach ($this->_meta_box['fields'] as $field) {
            $name = $field['id'];

            $old = get_post_meta($post_id, $name, true);
            $new = $_POST[$field['id']];

            if ($field['type'] == 'file' || $field['type'] == 'image') {
                $file = wp_handle_upload($_FILES[$name], array('test_form' => false));
                $new = $file['url'];
            }

            if ($new && $new != $old) {
                update_post_meta($post_id, $name, $new);
            } elseif ('' == $new && $old && $field['type'] != 'file' && $field['type'] != 'image') {
                delete_post_meta($post_id, $name, $old);
            }
        }
    }
}
?>