A scenario/campaign idea, taken from the headlines and a favorite book:
Right now, the finances of most of the First World nations are something of a joke, and a bad joke at that. It'll just take a little nudge to push them over, and there are all sorts of entities in the Dresdenverse who would do that for money, for sport, for a cause, or even just for the lolz.
The basic idea comes from the Spider-man: Secrets of the Sinister Six trilogy: In this rather excellent but sadly hard to find trilogy, a villain named the Gentleman has a plan: attack the foundations of the economic system, using an EMP to wipe out all financial computer records in NYC, and using a plot device Catalyst to destroy all of the written records (the Catalyst would bleach any ink within about 20 miles of the airburst point). Doing this in NYC would make a bit of a mess.
Thinking on it, this general concept could be adapted for a campaign arc or a scenario in the Dresdenverse very easily, depending on where you set the opposition's preparations and power level.
For preparations, a thaumaturgical ritual would need links to every kind of ink used within the target area--including the very hard-to-acquire U.S. Mint ink (which could be a scenario in-and-of itself). Additionally, a method of powering a city-wide hex-blast would need to be done.
For antagonists, everyone from the Denarians to the Reds to a warlock cult are options, although this feels more like something the Denarians would try and pull.
And if the PCs don't manage to stop (or manage to pull it off, depending on personal tastes) this? Financial collapse. NYC would be in city-wide anarchy. The dollar would likely fail, and possibly pull down other economies with it.
So. There's the idea. Feel free to use it, abuse it and detail it as you will; as I've already said, it's not original to me.