A simple lift sign plugin would be really nice, especially when making large multi storey buildings like a skyscraper in Towny, to save having to walk up and down multiple flights of stairs, we could make a lift sign elevator.
Here's a link to the plugin I have in mind.
http://dev.bukkit.org/bukkit-plugins/liftsign/
There are other more complicated lift plugins, but this one won't get broken by server lag.