Googsystray is a system tray app for Google Voice, GMail, Google Calendar, Google Reader, and Google Docs. It lets you keep track of the information provided by those services without having to keep a bunch of Web pages open or constantly checking them. It notifies you of new events, such as messages or alerts, and provides basic services quickly.
GCalert will access all your Google calendars and display alarms via libnotify for whenever you have alarms set for each event. These alarm widgets do not receive focus (and thus do not take keyboard input away from other applications), yet are clearly visible even on a cluttered desktop.