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