How to add a custom class or id to a menu
Menu Attributes is definitely a way to do this.

This simple module allows you to specify some additional attributes for menu items such as id, name, class, style, and rel.
You should use this module when

You want to &quot;nofollow&quot; certain menu items to sculpt the flow of PageRank through your site
You want to give a menu item an ID so you can easily select it using jQuery
You want to add additional classes or styles to a menu item

The module currently allows you to set the following attributes for each menu item:

Id
Name
Target
Rel
Class
Style
Accesskey