Large-scale energy storage has recently been discussed as part of the future of the smart grid because of the many opportunities for improvement in the reliability and quality of the electric grid that can stem from their use. Information exchange from utility to consumer and vice versa makes it possible to send real-time signals regarding electricity prices and consumption. This enables many applications such as arbitrage, electric reserves, and load following to be served immediately by energy storage systems that are on the grid. For this reason, large-scale energy storage technologies must be implemented that have the ability to serve these applications. This paper examines three energy storage technologies that appear to be well suited for large-scale implementation: sodium-sulfur, vanadium-redox flow batteries, and lithium-ion batteries. These technologies were examined along with many other current technologies and chosen due to the potential to operate at grid-scales. Also, several of their potential applications are discussed.