I know that Jews are supossed to give 10% of their income to charity, but what constitutes a charity? I know that Shuls, jewish schools and poor people in your community count, but what about secular organizations? There are some that save lives, such as the Red Cross. How about organizations that help children, perhaps a secular orphanage or Make a Wish foundation? Then there are the cultural arts, museums and zoo's. I'm sure the jewish defination of charities can's be as simple as the IRS' defination
Rabbi Yitzchak Breitowitz gave a lecture on charity a few years ago, and someone asked him this. He said the key was "providing for those who otherwise wouldn't have." An orphanage or library certainly does that. (He mentioned Catholic charities that have helped Jewish parents adopt a baby, too.) As for arts organizations, he asked if they provided something for those who couldn't afford it on their own.
He also pointed out that compared to "general" secular charities, Jewish charities have a much narrower donor base, so your donations might be needed more; but certainly the Red Cross or the like can count toward the 10% figure. And that different people will have different values for different causes and give accordingly; this is okay, and as a result, many different causes get funded.
I like Shalom's answer, I did want to clarify something: while certain contributions to a Synagogue would count as tzedaka, regular Synagogue membership dues do not.
This post gives also gives a very detailed explanation: http://www.pidyon.com/latest-writings/halacha/10-maaser/48-computing-maaser-how-much-tzedakah-charity-do-i-owe.html