One of my favorite menus to use is the Project Seven CSS Express Menus. I have quite often recommended this menu it if you need a dropdown menu and as an alternate to some of the commercial Expression Web add-ins. You can see an example of its use on my free Springtime Dynamic Web Template.
Cheryl Wise has posted a tutorial on her by-expression blog Project Seven CSS Express Menus in Expression Web. That same post also includes how to make changes to the graphics that are part of the menu.