Adding nice tooltips to wp-Nav_menu

Hi .. I have a theme which uses wp_nav_menu to create the main nav bar and I’d like to add a nice tooltip to each menu item describing what lies behind each menu item. I’ve added a custom walker and added the description from the menu but browser rendering of the title attribute is unpredictable and can’t be changed with CSS and so I’m looking for an alternative.

Is there a good WP plugin that will convert titles into tooltips or there another way to achieve the same thing as I already have the ability to output whatever I want with my custom walker ?

Thanks
Ron