I would like to see something like the Mob Spawner GUI mod for singleplayer. A simple mod that lets you change what mob spawns from the spawner. This would help ALOT in the making of dungeons.
the Mob Spawner GUI mod is a client mod. Bukkit is a server mod. A server mod cannot add a GUI in the same way a client mod can. This plugin allows spawners to be changed by use of a command (which is as close as you can get) http://forums.bukkit.org/threads/admn-fun-spawnmob-v1-8-support-for-ops-txt-531.6010/