Perhaps, it's one of the most frequency asked questions, but I'll ask again.
I have the next problem - as many methods I've tried, but none of them did not help me to change keyboard layout using ctrl+shift (in other words ctrl_shift_toggle). I've tried to do it using Control Center, setxkbmap and direct editing of /etc/X11/xorg.conf
This is my /etc/X11/xorg.conf (section for keyboard):

Section "InputDevice"

Identifier "Keyboard1"
Driver "keyboard"
Option "XkbRules" "xfree86"
Option "XkbModel" "pc104"
Option "XkbLayout" "us(nodeadkeys),ru(winkeys),ua(winkeys)"
Option "XkbOptions" "grp:ctrl_shift_toggle,grp_led:scroll"

EndSection

Distrib is Slackware 10

By the way, it seems like xorg keyboard section is not read properly, because after some system crashes, my us layout became basic (without nodeadkeys)

It was my problem too when I switched to Linux two years ago. Meanwhile I got used to kxkb, the KDE Keyboard switcher, a nice tool which shows the language in KDE systray too. It uses Ctrl-Alt-K as default hotkey but it's configurable. I set it to Ctrl-Alt-Space.