3mm red flickering flame LED

These are the LEDs you see in the flickering flame imitation candles so popular nowadays. They contain a red (625nm) LED and an IC that changes the brightness of the LED in a pseudo-random way to imitate a real flame, although it's not an exact imitation.

For a more realistic effect, using clusters of 3 or 4 of these is quite effective.

Note that these LEDs should be treated as a regular LED and used with resistors for voltages over 3 volts.