Oh, and more locally, Orrell Fussli has an english bookstore in the middle of Zurich, and sometimes has a small selection of english language books in their normal chain stores.
There is a large book shop at Sihlcity shopping centre in zurich, and they might also have a small range of english language books (I got a really nice kids cookbook there)...
And the Anglican church in Zurich has a book sale twice a year - once in the church hall and one at their Annual bazaar near Enge. I usually try to post the information on the forum when the dates are announced...
You can also try the second hand shops - I only know the ones in Zurich -
www.Tigel.ch - they usually have a small selection...