HiTechnic has released its Infrared Electronic Ball to go along with its IRSeeker. From the HiTechnic website:
This infrared electronic soccer ball is well balanced and emits infrared (IR) signals in all directions making it a great IR target that can be detected by the HiTechnic IRSeeker.
The ball is perfect for Robot soccer and other games and is approved by the RoboCup Junior Technical Committee for use in Robocup Jr competitions.
The ball contains 20 IR LEDs that are positioned to virtually eliminate blind spots and make sure the IR signal can be easily detected by your robot.
The ball is 75mm (~ 3 inches) in diameter and requires 4 AAA batteries (not included).