Distributed Sferics Sensors
From HacDC Wiki
Very nebulous idea at the moment, but the idea would be to build a distributed lightning detection system, with the intended goal of having precision high enough to go find the aftereffects of strikes (like geocaching). After thinking of this, I found some dutch folks have done much what I had in mind, so the problem is kind of a solved one. Still, it would be neat thing to make, and it doesn't appear to have a stateside equivalent yet (its sort of a public service project). Here is live data coming from the central European system.
I've heard the government runs these, but I haven't found any place the data is accessible online. If that's the case (and it's fairly high res) my enthusiasm for this idea is dimmed a lot.