Turns out, there are many: wood waste, cheese whey, waste sucrose, potato waste, brewery waste, and food and beverage wastes, just for starters. According to the folks over at the National Ethanol Vehicle Association:
The next generation of ethanol production facilities will include production from cellulose and biomass feedstocks. Earlier this year, there was a groundbreaking for a new ethanol production plant in Jennings, Louisiana which, when completed, will produce ethanol from rice hulls and bagasse. Three other plants are currently planned in California that will produce ethanol from rice straw.
Wait, did they just say straw? If only Rumpelstiltskin could see that.