I would really love to see something like a Day / Night Sensor block maybe an enhancement or just a filter that can take all EU's or even through redstone where you can turn off say power usage to certian power lines during the night or day on however the user sets it up. Don't forget the centre piece for crafting it would be a watch 
Theoretically, this could be done with a solar panel and an energy-o-mat. When it's light, the solar panel puts current into some circuit. If you hang the energy-o-mat off that circuit, it will power redstone.
The downside is that it's bulky and has to be exposed to the sky.
RedPower Sequencer ftw
As well Risugami should still have his ol Light Sensor around on his thread :3
