WorldBorder

[Lazybones]

http://dev.bukkit.org/bukkit-plugins/worldborder/

Seems like this would be a really useful plugin.. Would have saved us a lot of clean up and sprawl.

[Thorin]

Borders for specific worlds can be set to wrap around instead of just knocking back players who cross the border, instead sending them to the opposite edge of the border.

That's a really neat idea, so it's like a planet!  From spawn, travel east until you're back at spawn...

[Mr. Analog]

When I first tried Minecraft single player I thought that's how it worked haha I generated a huge strip of world and lost my first build