Watch Lightning Strikes in Real Time
As I write this, a line of thunderstorms is crossing Indiana, western Kentucky, Tennessee, and Mississippi. And there's a big storm in the Florida panhandle. How do I know? LightningMaps.org. It shows a live map with lightning strikes popping up a few seconds after they happen. The data comes from a network of monitoring stations and is visualized on top of a Google Maps view. As I watch, the delay is calculated at the top of the screen -- it's hovering between 4 and 5 seconds, so it may not be "real time," but it's close enough.
If you're curious, there's an extensive document (PDF) detailing how the system works, and how you can join the network.
See also: 7 Disasters Caused by Lightning; Slow-Motion Lightning; and Can You Really Tell How Close Lightning is by Listening for Thunder?