How to kill X?

[cr <cr@orcon.net.nz>]

Way back in the days of RedHat 5 or thereabouts, whenever X siezed for any 
reason, I could kill it with Alt-Ctrl-Backspace and end up back in the 
command line.   Very handy, since Linux is ~  10^6 times more stable than X   
;)

However, since I got more sophisticated hardware with an ATX power supply, 
Ctrl-Alt-Backspace turns the machine off (or reboots it), with consequent 
fscking of the drives, which is a pain.   

I just had a sieze in X, and Ctrl-Alt-F? had no effect, Ctrl-Alt-Backspace 
was the only key combination that worked.     Is there any setting that will 
restore its function of 'kill X but don't reboot the machine'  or any other 
key combination that achieves that?

cr