Yeah, what Lizzy said...
I do basic crunches, reverse crunches, double crunches (basic and reverse at the same time), bicycle crunches, and plank twists; that's all I can remember right now. I am working on side planks but I can only do about ten in a row because they are really hard for me. Pushups and plank stuff (like plank rows) also work your core. I have used Pilates too and did notice a difference. I am finally seeing some abs so it is worth the pain
You can probably get pics on how to do any you're not familiar with from Google, or from an exercise book.