I am a big advocate of core workouts for many different reasons. First of all, your core is such a large part of playing volleyball. You use your core for powerful jumping, you use it to reach when blocking, you also use it to swing when hitting. It is a muscle group that will impact so many of your skills and abilities. A great volleyball player will have a strong core.
Another huge reason that I like a core strength workout is that players are less likely to be injured when their core is strong. I have noticed that they tend to have fewer injuries and that is another huge reason to have a strong core.
Other reasons that I really like these workouts is that most of these core exercises will workout your entire body. By the time you are done, you will probably feel like you had an entire body workout.
Here a few exercises I love!
-Turkish get ups
-Squat and Reach Jumps