The SimpleMenu module for Drupal 6.x and 7.x offers a drop-down menu that inserts itself at the top of your browser window on your website.
The menu can be fixed1 or scroll with the page.
By default, SimpleMenu presents the Navigation menu in Drupal 6.x and the Management menu in Drupal 7.x. You can change the SimpleMenu settings to display a different menu and show it on another tag than the Body tag.
The following pages describe how the SimpleMenu can be setup and different known issues and how to handle them.