I found this interesting post on cleaning your coffee grinder.
If you aren’t drinking freshly ground coffee, you should be.
Ok, here is the tip from weeklyroast.com’s coffee blog, uncooked white rice.
A really great way to clean out your grinder is to use uncooked, white rice. If you use a blade grinder (and we highly recommend upgrading to a burr grinder!), fill it with white rice up to the blades. If you use a burr grinder, put about 2-3 teaspoons worth of white rice and set the burr grinder to a fine grind (espresso) setting and start grinding.
After you’ve finished grinding, you’ll notice immediately that large clumps of previously ground coffee are now clinging to the powdered, ground white rice and after dumping the grounds out, you should see spots you could never clean before coffee-ground free. The inside of the grinder should also be a lot cleaner than before as most of the old, rancid coffee oils also attached themselves to the white rice (they’re attracted to the starch in the rice – that’s why this technique works so well).
Repeat this process until the ground rice no longer has any black particles in it.