I tracked my Calories for almost 2 years. It was eye opening. But you have be certain you account for every little thing. Those tiny Snickers Bars and Hershey Kisses add up quick. As does that small bag of potato chips from the vending machine that was mostly air.
Livestrong had a good tracker that had a database of all the brand name foods you could buy at the time. But it was before Lance came out and told the truth, that I stopped going there, so I don't know what it's like today. There was another diet site that had a similar Calorie/meal tracker but I can't think of the name.