Dan is correct, there are too many to count. With my clients, I tend to gravitate towards exercises which force the core muscles to stabilize as external forces challenge proper alignment. For example, I have my client on the ball with head and shoulders, bridged, and then hand them just one dumbbell for a fly. I also love to use the foam roller, have my client lie lengthwise on it, cue them for a neutral spine and have them lift a leg off the ground.
I am sure you will get many more suggestions.