Wordpress - How do I include a TinyMCE editor in the frontend?

Well, Thanks to wp 3.3 now we have wp_editor() function to do that :)

editor_selector is for targeting classes, not ids.

Also, when using editor_selector, it is required to set mode: "specific_textareas" in order for it to work.

See http://tinymce.moxiecode.com/wiki.php/Configuration:editor_selector

So your JavaScript and HTML should look like this:

jQuery(document).ready(function(){
tinyMCE.init({
        mode : "specific_textareas",
        theme : "simple", 
        /*plugins : "autolink, lists, spellchecker, style, layer, table, advhr, advimage, advlink, emotions, iespell, inlinepopups, insertdatetime, preview, media, searchreplace, print, contextmenu, paste, directionality, fullscreen, noneditable, visualchars, nonbreaking, xhtmlxtras, template",*/
        editor_selector :"tinymce-enabled"
    });
});

<textarea rows="8" cols="40" name="description" id="editor" class="tinymce-enabled required"><?php echo $description;?></textarea>