A quick lighting of our jack o lantern this year, courtesy of 9 leds
I used three leds in series together with a resistor. I repeated this 3x to have three separate strands powered in parallel from a 9v battery. I included a switch to make it easy for the family to turn it on/off. In each series group there was a flicker LED, a very nice candle like effect, in green light for extra spookiness I used a piece of wax paper inside to help diffuse the light a bit.
FYI - The flicker effect carries over to the other LED's in series.
(sorry for the bad pics)