Menu Extras are those menus that appear at the right side of your menu bar (typically with icons).
You can rearrange them by command-clicking on one and dragging it left or right. Remove them like Dock items: Command-Drag away from the menu, let go and poof!
MenuExtras included with OS X are:
- volume,
- the clock (enhancement for this: http://www.scriptsoftware.com/iclock/ )
- battery indicator,
- AirPort indicator,
- Displays menu
- the Connection menu (see NetworkPreferences).
- iSync menu (iSync 1.0 web release)
Set any of these to display in the related SystemPreferences panel.
A few available from places other than Apple: ClassicSpy, ProcessWizard, MoonMenu, LaunchBar, ...
1 Advanced Hacking
There is a complex hack to change the colour of these icons: http://www.resexcellence.com/hack_html_02/07-30-02.shtml
Bscially, these are kept in /System/Library/CoreServices/Menu Extras
You can access the PackageContents and replace the icon files with colourized verisons of the same. (or replace them with something totally different!)