There has been an interesting discussion on tithing on the Well-Trained Mind boards. There are a large variety of Christians commenting there, so it's a helpful place to get a lot of different perspectives, especially since I've never discussed tithing with someone who is not LDS.
In the LDS Church, we are asked to tithe 10 percent on our gross income, and also asked to contribute to what we call fast offerings which specifically go to help people in need locally. We are then welcome to contribute to other things- like humanitarian aid, the missionary fund, money to build temples, etc.
There were several different points brought up- ones that you might hear in an LDS discussion on tithing too. First was the idea that tithing on our gross income instead of your net income would bring more blessings. Most of the blessings referred to were financial, and some of the posters there pointed out that we don't pay tithing to receive financial blessings. It's easier to see the financial blessings, but so often the blessings aren't financial.
Several posters felt strongly that tithing is not required anymore, and if you simply look at the New Testament, I think that's a reasonable conclusion. She certainly was not advocating that Christians not give, but that a specifically defined 10 percent was not necessary.
There was also a very interesting discussion about members of a certain church not feeling comfortable with what their church was doing with the money they received. It would be hard for me to feel like I was supposed to give money to an organization that I didn't feel like used the money very well.
One of the things I most enjoy about reading the WTM boards is that I gain new insights from other Christians.