EasyProps is a simple, bare-bones plugin that I wrote up that allows you to set server.properties from console or in-game.
I wrote this plugin so that OPs on my server could change server.properties without access to the actual file. I figured I'd release it in case anyone else would find it useful.
If there are any features that you think might be useful to add to this plugin, please let me know any I'll be sure to add them.
/props get <property name> - Returns the current value of the supplied property
/props set <property name> <value> - Sets the supplied property to the supplied value
/props list - Lists all properties in server.properties file