The Math Forum — If they don't have it, they know who does. All roads lead to the Forum. Every time I go there, I get sidetracked by something interesting.
Eric Weisstein's World of Mathematics — Formerly Eric's Treasure Trove, it now is associated with Wolfram. This is an on-line mathematics encyclopedia. Choose any math topic, and you will find a brief explanation, often with links to other relevant sites.
Jim Wilson — This is a mathematics professor from the University of Georgia. I like his site because he posts Geometer's Sketchpad challenges that are not too easy and not too difficult.
The Geometry Junkyard — Lots and lots of geometry links, compiled and sorted by David Eppstein of UC Irvine.
The Seattle Mariners — The only team.
ESPN — Why wait for the morning paper? Get the box scores now.
Billiard Congress of America — I could not call it fascinating reading, but this is the closest thing to a physical fitness program I have.
Yahoo Maps — Why is it that when people see you looking at a map, they think you are lost?
SimTel — An archive of shareware and freeware. Look here first.
Snopes.com — Urban Legends are an intriguing study. Snopes has an archive of legends, research into their origins and veracity, along with some incisive observations. To my knowledge, there are only two people working to maintain the site, but it has grown quite large.
The Skeptic's Dictionary — In the past, I certainly have found malarkey entertaining, but it is becoming less so. The turning point must have been the time a supervisor checked my surveying work with a pair of divining rods. The Skeptic's Dictionary is the best site I have seen for general information and references concerning a broad range of unfounded beliefs.
Movies — Search by title, subject, cast, director... Yes, I believe this is where the Kevin Bacon game started.