Amazon.com: HiLetgo 4 Channel 24V Relay Module with OPTO-Isolated Support High and Low Level Trigger for PLC Automation Equipment Control : Industrial & Scientific
4 Channel Relay Board - Electronics-Lab.com
4-Channel 5V Relay Module for Arduino DSP AVR PIC ARM
Handson Technology
5V Four-Channel Relay Module - Pin Diagram, Specifications, Applications, Working