I just read through this thread from the beginning. Interesting discussions - hoping to pull it back to the side of cordial. Ahem.
With respect to making the biggest philanthropical impact with your charitable dollar, look here:
http://www.impact.upenn.eduThey've done a lot of research already in different focus areas (hunger, health issues, child poverty, etc.)
A little background since I've been away from the forum for a while: Personally, my husband and I are not FIRE yet, but we realistically are close-ish under certain scenarios. I've got a serious medical condition that forced me to change my employment status to part time. This impacts a lot of things, including charitable cash giving due to incomprehensible medical expenses.
Our approach to giving is rooted deeply in our Christian beliefs, although we are not legalists. We were also raised in families where giving was modeled by our parents, both with their money and their time. And let me make clear that we do not come from money. I was the first woman on either side of my family to earn a college degree and my parents lived in a single wide trailer when they first got married. My husband grew up on a cattle ranch.
We are both fortunate and incredibly driven/hard workers. It actually legit brings us joy to be able to give. It's as natural as breathing to us. In the good years before I got hurt, we gave more (10-12 percent of gross). Lately, it's much less (maybe 3-4 percent of net). Our giving behavior would not change based on changes in the tax code.
Our giving over time has consisted of a combination of the following - think of it as a pie chart with each form of giving taking up different fractions of the pie based on our life circumstances:
1. Cash to our church (which we designate for allocation to particular ministries - children's ministry, international missions, and a program similar to Habitat for Humanity but the houses are built in our church parking lot then moved to the actual land in a specific neighborhood)
2. Time to our church (serving on committees, hubby helped build/served as a crew chief for 5 or 6 houses before I got hurt, I spent several weeks on a mission in Africa, writing content for the church website, etc.)
3. In kind donations to the LLS, a battered women's shelter and other charities that pick up at my home
4. Monthly checks to my 85 year old grandmother to supplement her Social Security
5. Cash and in-kind goods to various things at my kids' school that are charity related
6. Random requests for donations from friends
7. Time to non-church charitable organizations
This for sure has "slowed us down" regarding FIRE, but we feel strongly about charity, in whatever form, being a priority and modeling that for our children as well.
Sorry for length, I just wanted to give the OP a thorough answer.