What are good treats for horses?

Apples, pears, bananas, carrots, watermelon, pitted dates, and most all other fruits.

Hay cubes, oats, bran (etc), and alfafa cubes (made for horses).

Sugar(s) and Molasses are favorites of the horses themselves, but give these to them in MODERATION. They can do a number on their teeth and should be fed lightly!