With the increase in the penetration of renewable energy resources and advances in metering, communication and edge computing infrastructure, the importance and value of customer-side resources for the provision of transmission-level and distribution-level grid services has increased significantly. As such, this article provides a thorough review on different proposed modeling and control methodologies for selected customer-side resources and examines how each methodology meets the requirement for certain grid services both at the transmission and distribution levels. The services are considered from a competitive markets perspective. Specifically, commercial and residential heating, ventilation and air-conditioning systems (HVACs), water heating units, refrigeration units, batteries and electric vehicles (EVs) are the resources considered. Services considered include frequency regulation, spinning reserves provision, voltage management, deferral of transmission and distribution grid capacity upgrades, reliability and resiliency improvement. Finally, discussions on research needs regarding the usage of groups of heterogeneous resources for cascaded services are presented.