For joints, i hear most often about glucosamine and chondroitin. I have read reports from peer-reviewed journals that indicate they are not effective to a statistically significant degree, and I have heard anecdotally from people (and the results obtained in a dog we owned) that indicate they can be effective. I suppose it is possible that they work for some types of joint maladies, or maybe there s something about individual genetics/physiology that make them effective in some people and not in others. If my joints hurt, I'd sure try them, there doesn't seem to be a downside, other than the cost.
Other supplements: I take a multivitamin with a few extra antioxidants (no iron-men usually don't need it and it can have negative impact on heart health), I take 2 fish oil capsules every day, and I take one dose of Metamucil at night. I used to take more supplements (vitamin E, vitamin C, ginko, etc) but I don't think there's enough evidence of efficacy to make them worth the time/trouble/expense.
And lots of coffee.