used the ironmind grippers? YYEEAAAA BABBYY!! If used as proper training tool, with full closes, half reps, negatives, these can see you with instant gains, in strength and forearm size. Be sure to get a few, one easy warm up one, a working set and one you can work towards shutting.
I give my COC grippers lots and lots of love. That hard, grinding their handles together sort of love that they can't get enough of...
There's also the option of a leverage, um, thingy. Like when guys go oldschool and do 'feats of strength' with a sledge hammer, holding it by the end of the handle and levering the head up, or touching their nose. There's an exercise that I like that I do with my leverage bar. Standing, you hold your forearm out parallel to the floor, like you're half-way through a curl. You then rotate your forearm(while holding the leverage bar) supinating and pronating your hand. Can't go too fast, it's easy to pull something if you aren't used to the exercise. you can get a really good stretch in both directions, and there's no actual wrist flexion, you're just building mad supporting strength. And you get a bonus, because you're working you biceps in a novel fashion, because the biceps is one of the forearm supinators. You can also do this sitting, with your forearm resting on a bench or your leg.
I keep my lever bar under the coffee table, and do random exercises with it during commercials and such. Seems to really help with wrist health, if not forearm mass.
A lever bar is easy to make, and cheap, too. Get an old ten pound plate, or a five, or whatever is lying around. Then you need something for the bar. I used a standard plate, so I cut about two feet off an old broomstick. Wrapped duct tape around the end until it was built up a little less than half an inch, slid the plate on, and wrapped tape around the stick on the other side of the plate, trapping it in place. If you use an olymipic plate, you just use a hunk of pvc, and you get a thick handle bar. Or use a standard plate and use pvc with adapters to make the handle section any size. I wrapped my broom stick with some scrap vynil and contact cement until it just fit inside a piece of 1 1/2" pvc. It's a good size for a little grip work. Taped wrings of hockey tape around the handle, so I can keep track of where I place my hand. Give it an extra long handle, so you jsut move your hand to change the weight, instead of changing the plate.
Or you could just use a sledge hammer.