Coffee syrups are used by coffee shops all over the world to produce a wide range of flavoured coffee drinks from Vanilla Latte to Caramel Cappuccino. When choosing your range of coffee syups you should keep it simple and not just offer every flavour of coffee syrup available.
Market leading café chains like Starbucks use coffee syrups to great effect. They don't have a raft of flavours staring at you, but incorporate them into feature beverages called "signature drinks". Use seasonal coffee syrups like gingerbread at Christmas, a time when Starbucks have reported that every third drink ordered is a gingerbread latte.