add_menu_page(); as far as I can tell does not work with
screen_icon or the default CSS parameters. The
$icon paramater only takes 2 options, an
div (well 3 if you leave it empty), so that leaves you with these options:
Hard-code the link to the icons which are located in
wp-includes/images/wpicons.png. This is an image slice of all the icons.
Just cut out the icon you want in a photo editor and include it as a stand-alone image in your plugin folder like the codex example.
div parameter and define it via CSS. For example;
'custom menu title',
'div', //this part
To elaborate on the previous answer when using
screen_icon('edit'); here is the list:
You can also contain them in a div like :
<div id="icon-edit" class="icon32"></div>
Style reference: http://codex.wordpress.org/User:Wycks/Styling_Option_Pages: