Mom: Here's the mother of all calorie databases, at least in the U.S. it's generally where all the calorie sites, books, etc., get their figures.
You might also like www.CalorieKing.com.
There's a searchable database that is pretty much identical to the USDA's. The Calorie King is dietician Allan Borushek and the site is Australian. You can also buy a really substantial little diet guide he puts out: "The Doctor's Pocket Fat & Carbohydrate Counter." IMO, this is the best calorie guide in print. It's updated each year and I've bought them for approximately the last three. It's the U.S. edition and it's also got lots of capsulized info on diet, exercise, and various things such as diabetes, osteoporosis, fat, fiber, high blood pressure & more. You can also buy software for PC and Palm with all this stuff on it, but you don't need it as the site is so comprehensive and FREE!
There's also something called The Calorie Control Council. I don't have the address but you can find it. It's got a database, or did the last time I saw it.
Dietwatch and Cyberdiet.com used to be among my favorites. They also have lots of tools for calorie counting (based on the USDA data, though they don't tell you that). But they're now a paid site and I don't intend to pay for things that are free elsewhere.
There's a ton more, but the USDA is probably the most useful, in my opinion, especially for basic foods.