A Jacob’s Ladder is very easy to make. All you really need is a high voltage power supply, two metal rods, and some kind of insulating support for the rods. The power supply only needs to be of a sufficient voltage to break down the air at the base of the V (5kV and up will do). It is the current that is important.

Source: http://www.geocities.com/mistertippy/schematics/jacobs.html