Britannica
Is It Any Good?
Written mostly by Nobel Prize winners, the no-nonsense articles are comprehensive and well-organized. The timeline feature is very cool -- you just click on a subject and scroll through its history. The main drawback of this site is that only members ($70 a year) can read entire article entries and get access to the online resources (dictionary, thesaurus, and news articles).

Become a member and get recommendations from other parents based on your child's age.