Here is my fully automatic sugar cane farm. It uses an RFtools sensor to tell when the sugar cane is 3 blocks tall, then it pushes the blocks out behind the sugar
Sugar Rush! How to Make an Automatic Sugarcane Farm in Minecraft « Minecraft :: WonderHowTo
Minecraft: How to build a Fully Automatic Sugarcane Farm, Tutorial for 1.8 - video Dailymotion
How to Make a Fully Automated Sugar Cane Farm
Minecraft: How to build a Fully Automatic Sugarcane Farm, Tutorial for 1.8, simple, compact - video Dailymotion