Some of my favorite things:
Arts
Extraordinary Popular Delusions and the Madness of Crowds
Josefov, the medieval Jewish quarter in Prague
Science and mathematics
Radio astronomy and amateur radio
The S3 Project: Sounds and Sights of Science (U. of Chicago)
Philosophy of science preprint archive at Pitt
Joseph Mileti on the different sizes of infinity
Build your own 5-associahedron, courtesy Eugenia Cheng
Harvard Natural Sciences Lecture Demonstrations