Bartleby's online edition of the Columbia Encyclopedia

The Encyclopedia Britannica is available by subscription. But the classic 1911 edition of the Encyclopedia Britannica is online for free.

Encarta looks a good bet too.

The Getty Thesaurus of Geographical names.

A listing of online Encyclopedias and online Dictionaries at Oregon State University

Lexicool.com's dictionary search engine currently has links to over 3500 bilingual and multilingual dictionaries and glossaries freely available on the Internet.

Freelang is a place where you can download free dictionaries.

A good English French / French English dictionary originating in the UK.

The online Century Dictionary (includes an encyclopedia section)

The Merriam-Webster Dictionary.

A whole page of dictionary links at Your Dictionary

Bartleby's online edition of the American Heritage Dictionary

The 1913 Catholic Encyclopedia can be useful for timeless topics

If you need a list of every kind of rock, mineral, gem etc in English see The Mineral and Gemstone Kingdom.

To find out the comparative value of British money since 1670. (use MS Explorer if Netscape cannot read pound signs)

A set of resources related to comparative values of money worldwide.

A list of medieval prices.

Very detailed maps of many countries at MultiMap.com

A very good online atlas is the World Atlas on Gheos Travel Guide

Catholic and Orthodox Dates of Easter etc. past and future