whatever floats ya boat
squats will make your forearms bigger as well...how does that grab ya?
Agreed.
Try reverse grip curls with your thumb over, like a hook grip, really tears up the forearms.
I'd also try some dead hangs.
Step 1: Hang from a pullup bar
Step 2: repeat step 1 for desired time
also you can try some stongman holds, pinches, using various bar widths, farmers walks......tons of good stuff!