Cesium is most widely used by the oil drilling industry as a fluid lubricant for the drill. Cesium in other forms can be used by the medical community as it has a 30 year half life.
One application that we can all associate and understand better is it's use as a propellant in early ion engines used on space ships during long missions.
We don't hear of cesium too often because it is quick to react and explode and therefore presents a big danger to life when exposed to the wrong elements. For example, cesium rapidly corrodes glass and once it is exposed to water it will ignite. The air we breathe can posess enough humidity(water) for cesium to explode.