Yeah as long as you have flexion with a neutral spine, the exercise is fine. For example, jackknifes or hanging leg/knee raises. Checkout this article by Mike Robertson:
http://robertsontrainingsystems.com/...core-training/
same article with videos embedded, but less photos:
http://www.t-nation.com/free_online_...ore_training_1
Some of the "why"
http://robertsontrainingsystems.com/...ding-your-abs/
http://robertsontrainingsystems.com/...r-abs-part-ii/