If you are looking to add excitement to the traditional abdominal crunch, consider rope climbers. In this exercise, the abs go through a similar range of motion as the classic ab crunch. However, two things make this exercise unique. The first is the "rope-pulling" motion. The second is the range of the upper back and shoulders. They come up a bit higher than in the crunch.
Start with the back flat on the ground with knees bent. Crunch the abs. But as you do so, pretend you are pulling yourself up with a rope. Alternate back and forth between climbing hands and be sure to breathe out as the abs contract. The neck should be straight and chin up. Rope climbers work great when done as the last in a series of abdominal exercises. You will definitely feel a burn.
Lie flat with hands in the air (as if to pull a rope).
"Climb" the rope. Crunch the abs. Shoulders should come off ground.
Repeat the exercise.