If you miss the basic html edit window from TinyMCE (like me), there's a simple way to get it back.
Edit tiny_mce_config.php that is in wp-includes/js/tinymce and add 'code', just after 'wp_help', around line 32 (a very long line). You may also want to swap 'wp_adv_start', and 'wp_adv', to get the button that turns the rest of the editing functions on. The whole thing should look like that:
'wp_help', 'code', 'wp_adv', 'wp_adv_start',
Of course that won't fix the problems with all the P tags popping up here and there and the disappearing DIV tags. This post explains how to fix them: http://wordpress.org/support/topic/102799
