Xwindows crash

[Douglas Royds]

While I was mucking around in Nautilus last night, things crashed so 
spectacularly that I had to resort to the big red button. None of the 
normal Gnome keystrokes like Ctrl-Alt-Tab, Alt-F1, or 
Ctrl-Alt-RightArrow worked any more.

I recall from somewhere that there is some magic incantation (the 
Penguin's 3-fingered salute) that can get me out of this Xwindows hole. 
Anyone?

Thanks,
Douglas.