RFTools Spawner
With this block you can spawn many kinds of mobs. Using it requires a bit of setup work though. First you need a full syringe for the mob that you want to spawn. If you insert this syringe in the spawner UI you can then see the other items you will need to spawn a creature of this type.
To get the materials into the spawner you need to set use Matter Beamers.
Infusing the spawner reduces the amount of RF needed for spawning a creature.
The maximum rate of the spawner is limited to 1 creater per tick provided you can get enough material sent in it.
Here you can see the GUI of a mob spawner containing an Iron Golem Syringe:
