Racquetball is one of the best exercises around. Get a full-body aerobic/anaerobic workout while taking your aggressions out on a little rubber ball that can never get more than 40 feet away from you. Better yet--you get to do it with a friend.
According to the United States Racquetball Association:
The average number of calories burned during racquetball play ranges from moderate at 640/hour [Prevention, 1995] to 794/hour [Men's Health, 1995] -- to a high level at 13.7 per minute (or 822/hour) [Sports Training Institute].
An average game will take 20 minutes, during which a player will run a distance of approximately 3,650 feet -- or over two miles in one hour of play. [U.S. Olympic Training Center]
Racquetball players work at a constant rate of 75 to 85% of their maximum heart rate for the duration of a typical racquetball game. [USRA Elite Training Camp, 1992]
Racquetball offers both aerobic and anaerobic benefits, with both sustained high level heart rate activity and quick bursts of energy required during play.
Racquetball works nearly every muscle group, including sustained, repetitive use of large muscles that increase calorie burn and reduce fat percentage.
This information was taken from this page on the USRA site