Calendar Zone
http://www.calendarzone.com
Everything imaginable about days, years and months.

Fugitive Facts
http://www.hennepin.lib.mn.us/pub/search/fff_public.html
Hennepin County Library has the hard-to-find facts here.

How Stuff Works
http://www.howstuffworks.com
All you need to know about everything technological.

Information Please
http://www.infoplease.com/
The interactive almanac.

Library Spot -- Encyclopediae
http://libraryspot.com/encyclopedias.htm
All kinds of encyclopediae can be found here.

The Old Farmer's Almanac
http://almanac.com/
A source of useful information since 1792!