I've been trying to pay more attention to my core, and today I used 2 Bosu Balls for planks and side planks.

I did 2 sets of moving side planks with both my hand and my feet on Bosu Balls.  You can check out the exercise at ab-core-and-stomach-exercises.com

Core training is important for overall health, protecting the back from injury, improving posture, and improving sports activity.
 
Here are some core workout tips.

One of the biggest mistakes in Ab Training is neglecting the lower back.
Lower back exercises complement ab exercises.  In an effort to get a strong core most people focus exclusively on the abs, and forget about the lower back.
Don't forget to include lower back exercises in your workout.
Learn tons of Lower Back Exercises