I'm not aware of any of them being poisonous, but many of them don't taste nice, especially the fruit of ornamental species.

But you may have to be a little careful about what you mean by cherry. The term cherry covers a number of species, being a particular subfamily of the prunus genus. http://en.wikipedia.org/wiki/Cherry gives a list of about 40 species.

There is also Prunus laurocerasus, cherry laurel, a very common evergreen hedging plant, which although a Prunus and called a cherry, isn't strictly speaking a cherry. I've always thought of this one as being poisonous, but on checking just now apparently you can even eat the fruit of this one, even though the rest of the plant is poisonous, though whether you'd want to eat it is another matter. But it is very similar to, and often confused with, Prunus lusitanica, whose fruit is rather doubtful, but usually tastes sufficiently horrible that you probably wouldn't eat it in error.

And there is also Prunus cerasifera, the cherry plum, which a plum rather than a cherry. Which is delicious.