This is a fun, productive drill, especially for younger kids, though older kids can gain benefit from it, too. It focuses on the importance of getting rid of the ball in a hurry.
Split your squad into two teams. Line the first team up, one behind another, at the shortstop position. Take the second squad and place them behind first base. Next, place a five gallon bucket upside down on first base (a garbage can also works as a suitable target). Make sure that you have plenty of baseballs handy!
A coach rolls or hits a ball to the first person in line at the shortstop position, who then has three seconds to pick up the ball and throw it at the bucket. The coach should loudly count off the seconds; this will initially fluster some of your younger players, but will also help them to cope with pressure better in the long run.
If the bucket is missed, the player behind first base fields the ball and returns it to the coach. Regardless of the outcome, the player who made the throw rotates to the back of the line.
After several passes through the line, switch sides. As an added bonus, keep score between the two teams - it is amazing how much more effort you can get out of a kid if he's competing against his friends.
If you have enough coaching help, you can vary this drill by having both teams throw at the same time; the competition is a big hit with players.
This is a great drill for practice on throwing accuracy, quick release, and for encouraging quick decisions. Make it a part of your drill rotation.