Glucosamine at 1500 mg/day. I think it normally comes with chondroitin, though you can get it with even more crap thrown in.
I started taking it two months ago at the recommendation of a lot of bodybuilders. My knees have hurt for years (mildly), but enough that I couldn't consistnetly run without hurting them.
I've since been running quite a bit with very little discomfort. I can't say it's entirely that stuff, as it may be due to less weight, or them getting used to it or whatever, but I've been contented enough to at least continue with the stuff.
I also have had back aches for years and in the past month my back is 99%. Again, I can't contribute just to glucosamine as mainly it's used to treat hip/knee issues, and I've also dropped a bit of weight plus been working my back (so it's impossible to say what really the cure has been), but anyway an orthopedic surgeon I spoke to recently said that a lot of people have found it's helpful, and that it has no apparent long term effects even in large doses.
Walmart sells it cheaply.
So anyway, I'm going to continue using it full strength for at least another month and will then taper back on it to try and determine if it really has been the reason my aches hurt less, or if maybe something else is going on, but for now the outlook from it looks quite positive.
I've read only a little on it, but apparently it's a regenerative compound, so it theoretically actually heals things instead of covering them up like a pain reliever does.