Jimmy Carter on the Colbert Report: the Bible says you don't charge interest to a poor person

You probably knew that.

At this site I found a couple good quotes. This (Deuteronomy 23:19-20 ESV):

“You shall not charge interest on loans to your brother, interest on money, interest on food, interest on anything that is lent for interest. You may charge a foreigner interest, but you may not charge your brother interest...

That's pretty direct. And this one (Proverbs 28:8 ESV):

Whoever multiplies his wealth by interest and profit gathers it for him who is generous to the poor.

which sounds like moral justification for progressive taxation.