You're probably talking about pain in general, however for hangovers specifically I find aspirin is much more effective than ibuprofen. After a trip to Osaka several years ago I was told by my GP that I can't touch NSAIDs any more - I'd stripped my stomach lining from taking them too regularly. Well, in conjunction with Japanese whisky.

Anyway, I discovered a very unusual treatment for hangovers in my desperation: Melatonin. Not just any Melatonin - slow-release low doses. My sinuses would relax, intraocular pressure would go down and headache would cease. It had an anti-inflammatory action. Having read that Melatonin reduces intraocular pressure was what made me try it in the first place.

It works best when combined with caffeine, chiefly because you'll fall asleep otherwise but also because caffeine tends to help with hangovers as well. If you're ever deathly hungover take a stack consisting of slow-release Melatonin, 1000mg aspirin and a few cups of coffee or some caffeine pills. Avoid regular Melatonin - it's too strong and is not safe to use when operating a vehicle.

EDIT: I should clarify that it's not effective for prophylaxis - you take it when you wake up. Also note that taking a sleeping-aid on the night of drinking might be a death-wish. Wait until morning.