Two small DC motors with a round mirror glued to the shaft under an angle are hit by a 5V laserbeam.
http://www.aliexpress.com/item/Free-shipping-10P-5V-650nm-5mW-Laser-Red-Dot-Module-red-laser-sight-red-laser-diode/32354307065.html
By changeing the speed of one of the motors Lissajous patterns are projected on the ceiling. The motor diameters can be adjusted in the SCAD file, where they are clearly indicated.

If you run it with Arduino, try this one:
int M1 = 0;
int M2 = 1;
void setup() {
pinMode(M1, OUTPUT); pinMode(M2, OUTPUT);
}
void loop(){
analogWrite(M1,255);analogWrite(M2,200);delay(100);
}