We describe several different methods for generating the entangled ancilla states that are required for linear optics quantum computing. We show that post-selection can be used in combination with linear optical elements to generate the entangled ancilla, but with an exponentially-small efficiency. Alternatively, the ancilla can be efficiently generated using solid-state devices consisting of quantum wells coupled with tunnel junctions. Finally, we consider the possibility of using encoded ancilla in order to reduce the effects of decoherence and measurement errors.