Comment below rating threshold, click here to show it.
Singed has a circle he can throw that continually slows enemies.
Anivia has one that continually slows and damages enemies.
Even the new champion Graves has one he can throw that continually blinds enemies.
Akali has one that buffs and makes her invisible while slowing enemies.
Nasus has one that removes armor from enemies
Maokai has one that absorbs damage
Janna one that heals
Sometime later, we should make a champion with a special circle that silences all units inside for 0.5 seconds after leaving it and for as long as they stay inside it. I think it would be a pretty cool concept, a sort of area denial for casters, while having little to no effect on autoattacking champions.