Cable side bends, Wood Choppers, Russian twists. DB and BB side bends, Saxon Sides. Varoiuos angled leg raises or rolls that go from side to side.
My personal Favorites for the side work is the Wood Choppers and the cable side bends HEAVY. Really concentrating on Flexing the core as Hard as possible. \
Oh CT has a few Articles on abs as does His Girl Friend Christane they are both worth looking into in the library. Do an author search
Hope that helps,