A recent article published in PC Magazine, lists 100 web sites that are useful or entertaining and that most people don't know about. They include:

Netcraft.com which provides information about any web site's operating system, type of service and netblock owner.

Surprise.com which helps visitors pick out gifts by choosing occasions and/or personality traits.

Airsafe.com a database detailing every fatal aviation even for the last 31 years.

UselessKnowledge.com, a massive compendium of information, including quizzes and a random trivia generator

Visual Elements Periodic Table displays the periodic table graphically with information about each element. The graphics are fantastic!