"Incredible nutrition website" may sounds contradictory (at least if you're not obsessed with the properties of foods), but this one is truly amazing: nutritiondata.com. It's got a great database with all basic foods included (probably based on the USDA data) and a lot of other fast foods and whatnot included also. There's cool graphical analysis of the properties of various foods (for instance, how good they are for weight loss or gain, how nutritious they are, how complete are their proteins, what their ratios of fat/carbs/proteins are, and how they satisfy all of your vitamin and mineral needs).
It's all free. It seems to be supported by advertising. And you can add it to your Google toolbar, if you use that, or connect it to your search dropdown in Firefox.
But, seriously, stop reading all my blather and go there right now: nutritiondata.com. Even if you don't need or want any of this information, it's just fun to play with. Seriously. I could do it all day.