Optoisolator - 4 Channel
Cost: $2.25 each
Description: Opto-isolator with transistor output for interfacing to noisy loads. This 16-pin dip can be used in conjunction with relays, small motors, etc. to allow a simple microcontroller to turn on and off up to 50mA per channel.
Datasheets: PS2501 Datasheet, Example Schematic