Global navigation drop down menus in SharePoint 2010

1. Navigate to the publishing site that you are looking to add drop down navigation to.

2. Choose Site Actions > Site Settings > Navigation. Navigation can be found under Look and Feel.

3. You are now at the Navigation Settings page.  If you are at a top level (parent) site, you will notice that in the Global Navigation section, the default selection will be "Display  the navigation items below the current site".  This is because there is now site above this level to inherit from.

You will also notice two check boxes:

1. Show subsites - this will display any subsites that are child sites to the current site.

2. Show pages - this will display any pages are child pages to the current site.
 

Select the appropriate boxes to accomplish your goal.
 

4.  This is site level setting, which will require that you follow this same set of steps for each of the sites you want to display subsites and/or pages for.  Within each child site, you will also have the option to:

1. Display the same navigation items as the parent site

2. Display the navigation items below the current site.

Tip: In most cases, users expect to have navigation remain constant as they move through a site.  In this case you would choose to display the same navigation items as the parent site.

5. Select OK to save your changes.  Your menus will now look something like this...