Having a handy Reference Folder in your bookmarks is an absolute necessity. Let's start building a list of a few of the essentials you might consider putting in it:

(We'll be continuously adding to this list....)

A good Technical Language Dictionary Site
(or just go to the Location Line on your browser and type whatis )

Acronym Finder

Quick Look-ups for Area Codes ( or and Alternate Area Codes site ) and Zip Codes
More Area Code listings.

Everything you ever wanted to know about Area Codes

Area Codes and Country Codes

Find Any Country In The World

Find International Calling Codes from/to any country set.

Find the "local" time for any country/region in the world.

International Telephone Directories from more than 170 countries.

RefDesk.com - the best single source for Facts on the Net.

Information Reference Library from Simply The Best