The movements I have found to be most useful are barbell military press, these really force your wrists to work hard. Dumbbell clean and presses and of course fat bar style barbell curls. Particularly on the barbell curls they work parts of your forearm and grip strength you typically have not felt before when using a regular bar. They are great as you can easily fit them into your gym bag and totally change the feel of your workouts that you have been doing at the gym. You will find that on things like curls for doing thick bar deadlifts you will struggle to use the type of weight you may be accustomed to when using a regular bar.
You have probably seen plenty of videos of the strongmen at the Arnold expo trying to lift the circus dumbbell with it's really thick handle. the beauty of these Fat Gripz is you can recreate your own circus dumbbell or the inch dumbbell just by putting them on your dumbbells. This is a lot of fun and absolutely excellent way of working your grip strength.
Without any hesitation I would recommend Fat Gripz. They make your workouts fun and challenging as well as adding a great deal of variety to your regular workouts.