I bought the Cloud Star Dynamo treats - skin/coat, hip/joint and tummy treats. No idea if they really even DO anything, but meh, figure they can't hurt and they're a nice bed time snack.
I used to sprinkle Plaque Off on his food but once it ran out, I never bought more lol. I keep meaning to buy more.
I was also giving him a bit of salmon oil for a while.
But overall I just find them unnecessary. I don't really notice a big difference either way so it's kind of a hit or miss, or whatever I feel like buying or have around the house.