The following are reference sources on the Internet, in no particular order:
The Merriam-Webster Dictionary is fully searchable and contains pronounciations, etymologies, and a thesarus.
Roget's Thesaurus is just what you'd expect.
Paul Brians has compiled an excellent guide to Common Errors in English.
If the document you're trying to read isn't in English, Babelfish can translate it for you.
Project Gutenberg is one of the original efforts to compile a coprehensive collection of public-domain texts in electronic format.
The Internet Public Library is a non-profit effort to create a meaningful online library. Their catalog includes many complete texts online. They make extensive use of Project Gutenberg texts.
Project Bartleby contains many excellent reference works and much classic literature, including Bartlett's Quotations and The Elements of Style by William Strunk.
Shakespeare is still a favorite on the Internet. One of the best online repositories of his work is at the MIT Shakespeare Page.
There are many sites that offer various ways to search the Bible. One is Bible Browser from the Brown University Scholarly Technology Group.
The Library of Congress provides a search of legislative information on the Internet through its Thomas site.
Similarly, the House of Representatives has a fully searchable Internet Law Library with the entire United States Code.
In addition to the House of Representatives' home page and the Senate home page, there are many resources for finding information about your elected representatives. One of them is CapWeb.
The United States Postal System providea a Zip code Lookup and Address Information.
If you need help on how to write a politician, geting chewing gum out of your hair, how to shop for car insurance, or any of a number of other things, Learn2 might well have what you're looking for.
Many sites offer various kinds of searches that essentially look up information in the phone book. USWest Dex is the online version of the printed white and yellow pages. Four11 allows you to look up telephone and e-mail information nationwide. (USWest Dex uses Four11's services.) AnyWho is a similar service. There are others.
Many sites also offer street maps and driving directions. Most are generated by MapQuest.
If you want to know what the weather is like where you're going, try The Weather Channel. For more detailed weather information, try Intellicast.
Don't worry if you're not near a computer when you want to use the Internet to check the weather. Just give Jupiter a call at 1-888-573-TALK (1-888-573-8255) and let MIT's computer check it for you.
If you don't like the weather where you now live, try Apartments For Rent or one of their competitors.
If you know where you want to live, and that's in orbit, you can check J-Track to see if anybody else is already there, and whom your neighbors will be.
If you're still unsure as to what a satellite is, or how old the Universe is, or anything else related to space, you might want to Ask a NASA Scientist.
Before you send that e-mail about the end of the world to all your friends, take a moment to check to see if it's really an urban legend.
Similarly, check to see if that new computer virus is really a myth, too.
Don't believe all the stories you read about foreign countries, either; check to see what the Central Intelligence Agency Publications have to say about them.
And if it's a physical constant you're unsure of, look them up at the National Institue of Standards and Technology.
Those of you taking chemistry rather than physics will perhaps spend more time referring to Chemicool, an online Periodic Table of the Elements.
If you need help working with the math involved in physics, chemistry, economics, or any of a vast number of other fields, you can find a calculator that will do the job for you at the Calculators On-Line Center.