I'll add my approval of the Allegra Lounge. The showers are great. Fantastic water pressure, and you can make the water as hot as you can stand it.

freeupgrade, here is a link to the Swissair site, showing layout of the terminals. Scroll way down on the page and you'll see info on location of the Allegra Lounge. As someone else mentioned above, it is right after passport control...to the left as you come out the doors.
http://www.swissair.com/service/airport/zurich.htm