F9: Open Gmail to send an email to your friend
F11: Start a call with your friend
F12: Stop the current call
ESC: Close the current window
ALT + ESC: Minimize the current window
TAB: Switch between multiple chat windows
CTRL + I: Same as TAB
SHIFT + TAB: Same as TAB but in reverse order
CTRL + TAB: Same as SHIFT + TAB
Windows + ESC: Open Google Talk (if it's minimized, or in the tray)