Using a Power-FET it is possible to build a very simple touch dimmer for low voltage lamps. Two drawing pins are used here as the touch contacts. The electrical resistance of your skin is in the order of 100 kΩ to 1 MΩ. The circuit operates as an integrator with a capacitor in its negative feedback path.
This configuration gives a relatively linear control characteristic. Once you have selected a brightness level, it will be maintained for hours if you use a low leakage (foil) capacitor.
Another feature of this circuit is that the harder you press on the contacts, the quicker the lamp brightness changes.