setxkbmap -layout "foo" -variant "bar" -options "gobble:dygook"
The problem is though that you need to know your layout, your variant, and your options. And they're not always straightforward. What command would you use for a US querty and German Dvorak layout where the Meta key is on the left Windows key and Ctrl is mapped to the Caps Lock key? If you knew the answer  without looking it up first you're scaring me. Stay away from children please.
A few days ago Carl Worth asked a few XKB-configuration questions on IRC and amongst other things this led to yet another complaint about the lack of a man page. Which I answered with the usual "feel free to write one". Except that a few hours later I suddenly had the epiphany: we already have all this data - GNOME uses it just fine for its own keyboard configuration panel. A little later some XSL had been beaten into submission enough for me to proudly say that we now have a man page that lists every single option that you can pipe into setxkbmap. xkeyboard-config(7) for president!
This will be available in the next version, scheduled for September 27. Until then, see the git commit here. Fedora users: xkeyboard-config-2.3-2.fc16 and xkeyboard-config-2.3-2.fc15.
 setxkbmap -layout "us,de" -variant ",dvorak" \
-option "altwin:left_meta_win,ctrl:nocaps" Obvious now, isn't it?