1.5V LED FLASHER
This will flash a LED, using a single 1.5v cell. It may 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. My circuit has been copied by Eleccircuit.com but my layout makes it much easier to see how the circuit works.

Source: http://www.talkingelectronics.com