For those looking for more information about ISIS, Patrick B. Johnston and Benjamin Bahney have published a summary of their findings on the group's finances, estimating that they are currently taking in some $1 million a day.
From the piece, in the NY Times:
...[The group's] money came mostly from protection rackets that extorted the commercial, reconstruction, and oil sectors of northern Iraq’s economy. The group also made considerable money through war itself, plundering millions of dollars from local Christians and Shiites, whom ISIS views as apostates.
We believe that ISIS will remain financially solvent for the foreseeable future. A conservative calculation suggests that ISIS may generate a surplus of $100 million to $200 million this year that it could reinvest in state-building.
The View series, mentioned below, shows ISIS the way it wants to be portrayed - which is scary enough. Imagine what it looks like to the people on the ground when the cameras are gone.