When the 1.0.0 patch came out, my old light system broke. It was based around the fact that lightstone was a solid block, and transmitted power through itself when a current was applied. In the most recent update, lightstone became 'lightglass' so-to-speak. This broke my previous design, therefor I came up with this.
1: This design is as good as I can get it. It's tileable, so if you plan on making strip lights or something else of that nature, it works for that.
2: You can change the speed to which the block changes. To do this you just adjust both of the two repeaters needed.
3: It's somewhat compact, you can fit these in the space between your roof and ceiling.
4: On the fastest setting, the block comes down one tick after the button resets.
From The Front
From the Back
Note: It's barely visible, but there's a redstone torch on the far side of the input block.