Good diet is what makes your horse really look shiney as well as good grooming, but for some extra shine you can use Show Sheen. You just have to be careful not to spray it where your saddle and girth goes since it will make it slippery.
Just be careful as Show Sheen dries hair out, and really isn't "good" for it. It does nothing more then create an artifical shine, which is great for the show ring, but detrimental for everyday use. After diet and grooming, I'd suggest a bath with a good stain repellent shampoo. Again, be careful how much. You don't want to sacrifice coat quality for shine, diet and grooming will produce a glossy coat every time. Our entire herd eats nothing but grass, hay and a bit of oats, and they're all blindingly glossy.
I personally use a product called Fiebings Satin Sheen, it's moreso for hair conditioning which I use on my Arab mares extremely long mane to help prevent tangles and dirt clumps, since it leaves the mane very soft without drying it out. However, much like Show Sheen, it's extremely slippery because of the protecting agents to repell stains and dirt. It works virtually identical to Show Sheen, at about half the price, and doesn't dry hair out as bad.
Lots of grooming!! I love what daily rubber currycomb sessions do for Scout's coat! I don't bathe him too often, since the shampoo can strip the natural oils from the hair. I also use a dab of corn oil on his feed, it helps his coat and keeps him "well lubricated" digestively as well. I have used ShowSheen, Vetrolin Shine, LaserSheen, and several other brands of shine/detangler. I don't really have a favorite brand, basically whatever is on sale, ha ha, it all works pretty well. Vetrolin kind of removed stains as well. Just remember, shine in a can can't replace a good, daily grooming. Also, if you have a light colored horse, grey or pale palomino, etc., you may not get the same kind of shine as you would on a black or a chestnut. His coat may be every bit as healthy, it's just not in the color of the hair to look like WD-40.
Interesting, Miko, I've never known show sheen to dry the hair out. Maybe I just don't use it often enough to cause any damage.
I think that's usually the case, as most people know it isn't a "conditioner", just a product to bring out luster. I've heard numerous people (and review ratings) talk about how bad it can dry out hair though, from all the silicone in it? That's how I found Satin Sheen, which does more real conditioning. I still only use it once every couple of weeks, but it's neccesary to keep that darn mop of hers untangled. I comb it every single day, and she's constantly getting into burr patches, so it's super handy!