infoplease -

This is a website that says it has "All the knowledge you need"
http://www.infoplease.com/
Here you can find Almanacs, Atlas, Encyclopedia, Dictionary, Thesaurus, Features, Quizzes, Timelines, Countries, and more.

Also listed are: World & News, United States, History & Government, Biography, Sports, Arts & Entertainment, Business, Society and Culture, Health & Science, Daily Almanac, a Homework Center, and even a Fact Monster with Kid's reference, games & quizzes!

One thing that you might want to do is look up the history for a given year, Decade by Decade, or see a Year in Review:
http://www.infoplease.com/yearbyyear.html
(Find out what happened on the year you were born, or print out a year's facts and include it in a birthday card.)
There's also a Perpetual Calendar here too, going back as far as 1583 and it can go clear into the future!