Google - Before you end another sentence with a question mark, first ask yourself (silently, please): "Can I Google it?"
Wikipedia - Almost as few errors as Encyclopedia Britannica. And it is free! And you can edit it!
How Stuff Works - Yeah. Just like it says.
Whois - Reverse IP lookup. Associate an IP with a provider and geographic location.
Dictionary - Czech joor sp3lling 
ASCII Chart - There are 10 types of people in the world...
National Weather Service - Screw Get the raw data.
Google Maps - No more excuses for getting lost.  
Symbols - If it isn't ASCII, try looking for it here.
Web Elements - The periodic table, online.
Prime Number Research - Break that 4096 byte key!
Eric's Treasure Trove of Science - Forgot an equation? Don't want to dig through your old notes? Do you like greek symbols?