General

Amateur Athletic Foundation: Olympic Primer - A legacy of the 1984 Los Angeles Olympics, this site is a treasure trove of information- as well as games.

ESPN.com

SportsNetwork.com

Sport! Science @The Exploratorium

Sports Illustrated for Kids Online

Baseball

Major League Baseball - The official home page of all major league teams.

National Baseball Hall of Fame & Museum

Basketball

Chicago Sports.com - Bulls Home Page

National Basketball Association

Football

National Football League

Gymnastics

USA Gymnastics Online

Hockey

National Hockey League

Martial Arts

Black Belt Magazine - The online magazine for all styles of Martial Arts.

Isshinryu Karate - Created and maintained by Shawn Mammon, currently ranked as a San Dan in Wyoming, this site is a good one for reference, history & techniques.

Order of Isshin-ryu Karate - "The Order of Isshin-Ryu is a fraternity of the students of Master Toby Cooling." The site is quite extensive covering history, techniques, definitions, instruction, creeds.

Soccer

American Soccer Youth Organization - The organization for organized youth soccer.  Includes links to local regions as well as sections for coaches, players and parents.

Usscoccer.com - Official site of  the U.S. Soccer National Teams, this site has current soccer news, match results, schedules and many features.

Tennis

Tennis - The International Tennis Federation's Official Website

Wrestling

Amateur Wrestling News