What pain medications are appropriate after a concussion?

NONE. The most important part of the post-concussion evaluation is "sensorium" and this should not be altered by drugs. Let us watch the person closely and see their un-drugged behavior.
Often not helpful. Over the counter anti-inflammatories (such as Motrin, Tylenol, (acetaminophen) aleve) can be tried and may help, however these are typically not very effective for concussion headache. Concussion headaches consistently respond much better to rest and decreasing stimuli (quiet, dim, calm environment). Take naps, reduce noise & stimuli, stay hydrated.
Tylenol (acetaminophen) only. No anti inflammatories like ibuprofen, naproxen, aspirin, etc after concussion. They may lead to increased bleeding risk. That's something you don't want in your head. Tylenol (acetaminophen) does not carry that risk. Talk to your doctor and be sure to be evaluated if you think you have sustained one.