This juggling balls are great for (young) adult that want to learn to juggle 3 balls. The NDjugglng balls are produced by YoyoSam and available through this link.
If you are looking for a ball to juggle 5 or more the Jugglequip is a great juggling beanbag. The medium size is great for most adults to learn to juggle 5 balls with. I recommend the small size for most people for 7-ball juggling.