This was a pretty interesting article about what not to compost or recycle. I was surprised at a couple, I would of and probably have thrown walnut shells and rice in my compost pile. I won't anymore. Apparently they come with the wrong kind of bacteria and attract pests.
Walnuts: These contain juglone, a natural aromatic compound toxic to some plants.
Rice: Cooked rice is unusually fertile breeding ground for the kinds of bacteria you don't want in your pile. Raw rice attracts varmints.