Kuiper Belt
Similar to the asteroid belt, the Kuiper Belt is a region of leftovers from the solar system's early history. Like asteroid belt, it has also been shaped by a giant planet, although it's more of a thick disk (like a donut) than a thin belt.

And:
Oort Cloud
The Oort Cloud is believed to be a thick bubble of icy debris that surrounds our solar system.

Never dull, always interesting, I think.