Systray.exe can display the following icons in the notification area:
Battery Meter
PC Card Status
Volume Control
Quickres
Task Scheduler
Other programs can also add icons:
Windows Explorer adds a printer status icon.
Exchange or Outlook adds a mail status icon.
The Accessibility status indicator program (Accstat.exe) displays keyboard accessibility icons.
Microsoft Fax adds the Fax Rendering and Fax Status icons.
NOTE: See
How do I hide System Tray (Notification Area) icons in Windows XP?