Infoplease: All the Knowledge You Need  facts, resources, and activities on a variety of subjects.

Farmer’s Almanac  Covers astronomical events, weather conditions and forecasts, recipes, and gardening tips.

GeoHive    global statistics, country profiles and regional profiles.

American Heritage Dictionary of the English Language, 4th ed

Cambridge Dictionary of American English

MedTerms medical terminology

Online Etymology Dictionary origins of words

Rhyming Dictionary

Merriam Webster