I came to bukkit with a very brief knowledge of java. At this time being I am lost with where to start when it comes to coding for Minecraft. I came up with this concept... Place a lever in a certain area and tell the plugin to 'once the lever is pulled in "so and so coordinates" it changes the time of day being day or night. Also you could incorperate loads of other things like a monster spawning in a certain place when a lever is pulled or anything really.
This may have been better posted in requests. This forum is for plugins which are written and are to be moved to the main release forum.