1.5v LED FLASHER
This will flash a LED, using a single 1.5v cell. It will even flash a white LED even though this type of LED needs about 3.2v to 3.6v for operation.
The circuit takes about 2mA but produces a very bright flash.
source : http://www.talkingelectronics.com.au/projects/200TrCcts/200TrCcts.html