Are you talking about for humans or dogs? I don't know much about giving dogs supplements, but for humans, I've heard raving great things about red yeast rice, and have started myself and my husband on it for high cholesterol.
In addition, it is recommended to take additional magnesium as well-- for high blood pressure, primarily, but it is recommended for many other things as well-- my husband has a herniated disk in his back, and I'm hoping the mag will help keep the inflammation and muscle spasms down so he can work better.
Another one that is recommended to assist the red yeast rice and the magnesium is Co-enzyme Q10. I haven't found that one yet, but plan to look for it.
And then there is garlic. Garlic is shown to be beneficial in reducing cholesterol, blood pressure, and boosting the immune system. It also comes in the form of odorless capsules, so you can still keep your friends close.
And of course, a good multi-vitamin, high in all the B vitamins, is a good start!
All that being said, all the supplements in the world cannot compensate for good nutrition (whole grains, fresh fruits and vegetables, and lean meats/fish), and exercise. That's where my dog is one of the best things I can do for my health! In addition, studies have shown that people who have pets have lower blood pressure, on average, than those without! Just the act of petting an animal reduces tension, blood pressure, respiration, and heart rate.
Live long, and prosper! : D