I think I figured it out. If anyone else wants to get a tax credit by donating their services to a church or another non-profit organization, just go to this IRS document:
http://www.irs.gov/pub/irs-pdf/p1771.pdf
It's pretty simple.
There are more detailed laws about it in this PDF:
http://www.irs.gov/pub/irs-tege/eotopicm99.pdf