http://slashdot.org/ is a site for geeks with news interesting to geeks. It has become very popular and gathers large crowds of people who read the posted articles and participate in various discussions. When a news story posted on this site appeals to a large number of Slashdot readers, the site mentioned in the news story often suddenly becomes a new mecca during the day the story was posted and the next few days. If the site's owner has just a small machine and never expected to gain such popularity in so little time, the server is generally unable to supply the demand and often dies. This is known as the Slashdot Effect.
Web Performance Tuning, by Patrick Killelea (O'Reilly).
The mod_throttle home page: http://www.snert.com/Software/mod_throttle/.
The mod_bandwidth home page: http://www.cohprog.com/mod_bandwidth.html.
The mod_backhand home page: http://www.backhand.org/mod_backhand/.