I have a 2005 Dodge Neon that is indicating misfires with codes P0300, P0303, P0304. The spark plugs and wires have already been changed. What could be the most likely cause?

Possible causes; Faulty spark plug (s), Faulty ignition coil (s), Clogged or faulty fuel injector (s), Intake air leak, Fuel injectors harness is open or shorted, Fuel Injectors circuit poor electrical connection, Ignition coils harness is open or shorted, Ignition coils circuit poor electrical connection, Insufficient cylinders compression, Incorrect fuel pressure.

It's an intermittent problem.

Then it is going to be electrical.

Look at the electrical causes above.

Would the coil pack be the most likely cause?

Thanks Tom, still haven't figured out how you do that...So the coil could have a crack, or weak, that can be tested at an auto parts store, spark plug wires would be the other most common. You probably should check compression first to know the condition of the engine before putting any money into it.