Just a couple farm designs I came up with one morning for simple automatic harvesting. These farms are designed to be completely tileable horizontally, be compact and use the least amount of redstone possible.

In the world save I built the sections for each farm, an example of them tiled, an example of them tiled with just the skeleton showing and then I built an example of how to hook them all up to a single switch. You will also find 3 books in your inventory giving you some basic information on each farm design.