Here are a few websites that I like:

Astronomy Picture of the Day

Cornell University

Fab Labs

Google Art Project

Google Maps Pedometer

Google Scholar

Granta Design Educational Resources

Key to Orders of Trilobites

Massachusetts Institute of Technology

NACA/NASA Technical Reports Server (for administrative reasons this is not always up for everyone, but there are mirrors for a lot of the content in various places like here).

NPR's Wait, Wait, Don't Tell Me!

Organic Farming Research Foundation

Cornell Lab of Ornithology Birdcams Project (Formerly Project FeederWatch)

Project Gutenberg

Resource Revival

Serious Eats

Sheldon Brown's Bicycle Articles

Stanford Encyclopedia of Philosophy

This-to-That

Udall Foundation

VassarStats

Web Plot Digitizer

Whitney Tool Speed and Feed Calculator

xkcd