KG-12 Copper Solvent
Recently I installed night sights on my girlfriend's Glock 26 and my new M&P. Since I'm a barbarian I used the old brass punch/hammer method. A year or so ago I had switched to KG12 copper solvent as I saw an impressive internet test on how effective it was. It's tough to quantify the effectiveness, since it does not turn blue or green when used in a barrel. But since my firearms shoot as well as ever, I've stuck with it.
So to get rid of the un-sightly brass punch marks on the sights, I used a q-tip and KG12 and after a few seconds of rubbing, the marks disappeared like magic I was very impressed because usually even "strong" copper removers like Barnes CR-10 take a bit of time to work like that. Understandably brass is not copper, but it's definitely worth a look.
I use this stuff too, I think it works great. My only complaint is the smell, but it is far less smelly than the ammonia based copper solvents.