Less is more when it comes to supplements.
For joints I have had great luck with Acti-Flex 4000. It's a liquid that's very potent. For maintanence, you can use 1/2 dose. Big D's has the best price on it.
For everything else, I get a custom blend from horsetech.com. Their flax base is one of the best out there and works very well for coat and hooves. Mine is a vit/min blend in their NutraFlax with extra magnesium for my "easy keeper" and moody mare. If you're not sure what kind of blend you need, they have a vit/min pre-done that you can have blended with 1-2 oz of the NutraFlax. I use 2 oz as my horses don't have a lot of grazing (provides good Omega 3's that are missing in hay).
They can also blend in joint supplements too, for an all-in-one product. I don't have all of mind on joint supplements, so I go with separate products.
To encourage my horses to drink water, improve skin and hoof health, and keep my boys "clean", I use 1/2 cup of Apple Cider Vinegar. It works well and I don't have to feed electrolytes. I get the cheap ACV from walmart, $3.78 a gallon.