Lasers are very common at raves and big nightclubs. It is a single concentrated light beam that is reflected off two ultra fast mirrors that move faster that the wings of a fly. This allows the unit to draw shapes from a simple circle to something complex like a picture.

The Urban Rhythmics Green Laser

Although lasers can be used to project images they are more commonly used for their ability to cut lines and shapes through smoke creating a massive variety of effects from gentle "sheets" of light hanging just above the crowd's heads (hence the common term "reach for the lasers") to rapid moving shapes and tunnelling effects.