Naturally, any exercise that requires grip strength will work your forearm flexors (the palm side of the hand/wrist unit). Exercises such as deadlifts, power shrugs and pull ups will have a lot of work in this manner. Modified grip so that the knuckle side is leading in exercises such as your curls and extensions will also work the forearm extensors isometrically (so, pronated curls and supinated tricep pulldowns, for example).
Beyond that, grip-specific exercises, as well as forearm curls and extensions, will specifically work the forearm flexors and extensors.