...and behind the back reverse curls with barbbell
for me this is the BEST!!!! can use lots of weight with good form. I agree forearms get lot of indirect work from back training, but my genetics suck for forearms and they only grow (and very little i mean) with lots of direct workout.
i prefer barbell, but use dumbells sometimes...reps between 12 and 15, lots of sets usually (4-6) 2 to 3 exercises...
Oh, a detail, nowadays im doing forearms EVERY DAY!!!!
(but with less volume than i said above)