Slimeball

The Slimeball is an item dropped by Slimes. There are currently no uses for it.

0-2 slime balls will be dropped when a small slime is killed. Only small slimes will drop Slimeballs on death, and larger slimes will divide into smaller slimes. (Beta 1.3_01 update changed it so that if an item that deals more than half a heart is used to kill a slime, no slimeballs will be dropped and the slime will not split into smaller slimes.) As slimeballs come from Slimes, they are a renewable resource.

Improvised Use until Update
Some users use these as tokens or cash in multiplayer servers, since it has no use and is more realistic and since server mods do not use up inventory space. When in Single Player, some players use them to show how many slimes they have killed. In some custom maps and challenges, they are used as score, or as triggers for pressure plates as the player is guaranteed to have no other use for them.

Mods
A mod was recently created, which allows a player to make arrows from slime, eggs, etc. The mod is known as Elemental arrows.