You can no longer add/remove indicators or panels by right-clicking like you used to with older Ubuntu versions before 11.10.

Warning: The default indicators (messages, networking, power, sound, user accounts, etc.) are tightly integrated with Unity since Ubuntu 11.10, and trying to remove them may cause problems.

• You can remove these default indicators without affecting the rest of the system:

  
  
  
  
  
  1. Messages: Remove package indicator-messages
  
  
  2. Sound: Remove package indicator-sound
  
  
  3. Power: Remove package indicator-power
  
  
  4. Print Jobs: Remove package indicator-printers
  
  
  5. Date/Time: Simply enable/disable from System Settings...Time & Date:
     
  
  



• Removing these default indicators is NOT recommended or not possible without serious adverse effects:

  
  
  
  
  
  1. Networking: Provided by package network-manager-gnome. DO NOT remove unless you have a desktop with one wired ethernet connection and do not use VPNs.
  
  
  2. User Accounts and System: Both provided by the package indicator-session. Removing this package will remove the Shutdown, Logout, etc. options as well!
     
     
     
     
     • Editing the list shown in the System Menu (Startup Applications, Printers, etc.) is NOT possible without modifying the source.
     
     
  
  

Adding other indicators

Please see this question for a master-list of all the different indicators -- each answer/comments will tell you if it is available from PPAs or the Software Center:

What Application Indicators are available?