I've used Aussie Hair Insurance Leave-In Conditioner on my own hair. I really like their products for myself... I haven't used it on my horse, but it's a spray so it might be convenient...
Also, if you go to a sally's beauty supply (or equivalent) you can buy a cholesterol treatment....leave it in for 5 mins and rinse out...talk about conditioned!
Sally's have a generic paul mitchell brand of their "super skinny". It is a serum that I leave in his mane and tail. Total shine, no flyaways and no tangles. Awsome stuff and only its only about $8.
Mane and Tail conditioner. The horse/people brand is a good one. I know of a lady who owns drafts and she leaves that conditioner then wraps up their tails. It grows like crazy, even works better than MTG.
I get the nicest smelling cheap conditioner that I can and mix it with water in a spray bottle. And spray through. Its just as good as the "proper" stuff I bought for $20.
I use Mane n' Tail ! It works great in Crickets tail. It can be used in wet tails , dry tails, it can be washed or it can be left in and you can use it in your own hair!