Triceps Pull Down: Activates the long strip of muscle within the forearm that connects with the triceps. Do these at a cable machine with a bar, and grip underhanded.
Decline Wrist Curls / Extensions: activates muscles in wrist and upper forearm. Do these at a decline to prevent injury by hyper extension. Use light weights. Heavy weights can cause permanent injury.
Flip Wrist to Failure: activates stabilizer muscles throughout forearm. simply hold dumbbells and support forearms with a flat bench. Flip your grip when you cannot maintain straight wrists any longer.