Yup, it is - I know the feeling when you can't find something like that though.
I'm not sure what you're running for a window manager or anything, but one of the following should do it:
Right click (or maybe left or centre) on the desktop, you should get a menu that has "Logout" or "Quit" or something on it.
Click the button on the taskbar (like the start button in windoze) and hit "logout"
Failing those, press CTRL-ALT-Backspace. (That ALWAYS works!)