The most common errors in Undergraduate Mathematics is a web page by Professor Eric Schecter of Vanderbilt University. It is not a list of humorous errors, but a careful presentation of mistakes made by students at all levels. I recommend it to all you.
The MacTutor History of Mathematics Archive from St. Andrews University.
The Mathematical Association of America
Patuxent Bird Identification InfoCenter A great resource for birdwatchers and listeners.
Sky Draw Interactive Star Chart from the Osservatorio Astrofisico (Astrophysical Observatory); Catania, Italy.
NASA Track the International Space Station, Shuttle, and satellites.
Heavens Above is another great site for finding satellites, stars, and planets. This link assumes you are viewing from Atlanta, Georgia (not Atlanta, Idaho, Kentucky, Indiana, or one of 15 other states), and the main Heavens Above page is here.
Time of Day from the U. S. Naval Observatory There are lots of interesting links here.
Professor Wang's Putnam Exam and Problem page.