The word for church in Russian is церковь. It is a third-declension feminine noun with a complication: the о drops out in every case except the nominative/accusative singular and the instrumental singular:

You will notice that there are alternative forms for the prepositional, dative and instrumental plurals: they can be soft or hard. The справка division at gramota.ru suggests both forms are acceptable, but I didn't really believe them because the soft versions should be much more natural by analogy with other feminine nouns in -ь, so I did a quick Google hit count (6 Feb 2010) and came up with these results:

So much for my theory. It seems like the hard forms are dominating.³ (Take that conclusion with a grain of salt. Such Google searches do not tell you how many times a particularly source is simply copied, so you can't tell how many unique instances there are of the word.) Despite the ambiguity, we can still produce some sample sentences:

¹ «Ни за что» means “not for anything” in the sense of “I wouldn't do it for anything in the world.” The ни and за are unstressed, and the что is stressed. Notice that there is a slight spelling difference (and a major stress difference) between that phrase and the phrase «не за что». In the latter the не is stressed the за and что are unstressed; it literally means “there is nothing for which” in the sense of “There is nothing for which to thank me”; we usually translate it as “don't mention it”: «Спасибо». «Не за что». “Thanks.” “Don't mention it.”

² This is an old stock phrase I encountered in Даль. People used it even though there were fewer than 1,600 churches in Moscow, so in effect it really means “There are a great many churches in Moscow.” Human languages often use large numbers to mean a non-specific “great many.” It is a common literary trope which we call “numerical hyperbole.” This use of language seems quite unnatural to those of us who were taught arithmetic from an early age and who were penalized if a number was off by even one. We tend to think “A number is precisely what a number says, nothing more and nothing less.” Alas, that is a common error in thought produced by otherwise good education.

³ Ah, it looks like my original guess that the soft forms are dominating is correct. See the discussion in the comment section. Thanks to the readers who gave such great feedback!