This stuff is harsh, smells like nothing other than industrial chemicals, and the label looks like a transplant from a cleaning shelf in the 1970s. But Bar Keepers Friend gets your pans clean when nothing else makes the smallest difference.
When you've applied a bit too much heat to a very sticky sauce or just used a frying pan repeatedly, you'll get the kinds of stains that laugh at your futile attempts with sponges and dish soap. They seem just below the surface of the pan, more like discolorations than blemishes. Put on some gloves, apply some Bar Keepers Friend and marvel at how powerful chemistry can be. The Not Martha blog has a great before-and-after demonstration of the stuff, and we've seen a can of the blue-and-gold on the shelves of the most skilled home cooks we know — because even a skilled hand can reduce a sauce just a bit too far.
Bar Keepers Friend runs about $US7 for 12 ounces on Amazon. Don't use it on cast iron, and do use it where you've got some ventilation.