At the last IDEA Conference, I attended a session on nutrition by Roberta Anding. I was very impressed by her suberb knowledge. She recommended the web site www.scandpg.org as the place to get reliable information that is well reviewed.
http://nutritiondata.self.com/ pros: provides a very helpful search for nutrition information from a large database of foods
cons: not sure what the source of this information is but it appears somewhat accurate and thorough