All nutrition guides and/or software uses the USDA nutrient database as the backbone. You can go directly to the USDA site at http://www.nal.usda.gov/fnic/foodcomp/ and click 'search' to look up something, or download their free software so you have the latest nutrition at your fingertips
Being Canadian, I prefer http://www.dietitians.ca/
If you register, it also has a counter / journal thingy where you can enter everything you ate each day, & see just how bad you really have been! Kind of like WW online, only free.