Good Strength Training for Abs (without crunches) ?

It's been mentioned above, but planks are pretty great for your core. Variations can help up the intensity. Side planks, extending leg/opposite arm, lower to elbows then back up to hands (can do this with one leg extended, etc.

Here are three plank workouts that may do the trick

https://www.youtube.com/watch?v=pvzaUmLaTjI

https://www.youtube.com/watch?v=6mV-c3u2KAQ

https://www.youtube.com/watch?v=3DNN9a5pU2A