I'm not going to lie, arms are amazing. They are the first thing people look when you are wearing a shirt, since they are the only noticeable part of your body that can tell them you lift. Don't get me wrong, biceps are really badass, but big forarms can be as aesthetic and give a stronger look to your arms.
The thing is, do you have time to train your forearms? If you aren't a bodybuilder than has a lot of available time at the time, you may not always have the time or even won't feel like working them out. Happily for you, you can develop these badboys without having to focus on them, ever.
Lift 'em corpses
I don't want to sound like a serial killer here, but lifting raw dead weight with your hands will greatly improve your forearms. Heavy deadlifts without straps puts stress on your forearms since your hold the weight with your grip strength even if it is a back workout. Exercises categorized in the Olympic weightlifting category, especially all of the clean variations, will destroy your forearms (in a good way, kids). You won't see an Olympic weightlifter with tiny forearms any time soon, I promise.
At some gyms, you can find thicker barbells you can use. Doing all curling movements for your biceps using a thicker barbell will force your hands to grip tighter so you won't drop it. This stresses the crap out of your forearms without you even thinking about it. You can also buy thick grips for dumbbells on the web so you can incorporate them in most of your workout.
Cable hammer curls, seated, incline or standing hammer curls, and reverse grip curls all does wonders for your forearms. This puts your hand in a position where it needs to stay tight to prevent it from collapsing down, making your forearms grow.