Religion hasn't done anything good or bad. People who follow different religions have done bad things and good things.
I would say the best thing that a belief does is give people a purpose. It really depends on the religion though, some religions do not give people a sense of fulfillment or a sense of purpose. I am a Christian who just recently began to follow Jesus. When I was an atheist I found life rather drab. I did not see a point to existence, and could not find any motivation. Another thing that ate at me was the inability to explain the world relying purely on current scientific knowledge.
Learning about religion led me to understanding Jesus. This has made all the difference. Honestly if you want to know what good religion can do, then spend some with some new Christians, and when I say Christian I mean follower of Christ. If they are not following what Christ laid out in Matthew through to Acts then you may not be getting the most accurate information. Take a look at the way their faith has changed their lives.
Trust me if they truly realize the implications Jesus brings to the table, then you will see some amazing changes in them, and the people around them, for the better. That is the good I see in Christianity at least.