There have been numerous performers at the Superbowl, not including the first few games that only had marching bands as the entertainment; some of the top performers include Katy Perry, Carol Channing, New Kids on the Block, Michael Jackson, Tony Bennett and U2. Prior to the late '80s it was not guaranteed that the halftime show would involve someone that was known in the music industry.
The late 80s saw a change in the halftime show programming with Chubby Checkers performing with the Rockettes and 88 pianos. The next year was a different type of entertainment act, but 1990 going forward saw only acts from the music business being scheduled. The change in the line up was made to help counter the programming that other channels were showing at the same time. Music really appealed to the viewers and drew in age groups and people who might not normally watch the halftime show or the ball game at all. The shows become larger and more extravagant every year.
While the artists are not paid for their performance, they are often compensated for their travel and expenses. Artist often see a spike in sales and popularity after a performance. These shows are now as much of a focal point of the Super Bowl as the game itself and a major point of ticket sales. The headliners are usually announced before the tickets ever go on sale.