[EDIT] In this thread, there may be broken links as time goes on. The purpose of the posts is to give members ideas to build on and be a repository for other people to add to as well. Happy building! Oh, let me add that I have no affliation to any seller or company. Always check out your suppliers before handing over your hard earned cash.
----------------------------------------------------------------------------------------------------------------------------
Well its new to me. I can see it now. "Dave, there seems to be an approaching storm. It's time to stop our soccer game and get inside" eBay Link, Datasheet Link

--------
Franklin Lightning Sensor provides early warning indication of lightning
storm activity within a 40km range
- Provides distance estimation to the head of the storm
- Detects both cloud-to-ground and intra-cloud (cloud-to-cloud) ashes
- Intelligent algorithm provides for false disturber rejection
- Programmable detection levels enable threshold setting
for optimal con gurability
- SPI and I2C interface is used for control and register reading
- Automatic antenna tuning
- Supply voltage range 2.4 to 5.5V
- Power-down, listening and active mode
-------




Here is another one for motion detection for up to 20 meters. *eek*
Microwave Doppler Radar Motion Sensor


Datasheet is here: http://www.apollounion.com/en/down.asp?filename=Upload/DownFiles/HB100.pdf

Edit: see post #6 for better one.

UPDATE: Here is another lightning detector that popped up.
eBay Link