RFTools Item Filter
The Item Filter is a block that allows you precise control of how items should be routed along the six sides of this block. Every side can be configured for input or output and the block has nine inventory slots that can be matched to these six sides.
First every of the nine inventory slots can be configured to accept only a specific item. To do that just insert the block you want in the corresponding ghost slot.
You can craft this block with the following recipe:
Here is a screenshot of the user interface for a setup to filter the output of a skeleton farm as well as a tree farm (in a single block!):
