Endnote X at least does have a sort of WYSIWYG in the style manager. If you open the style Manager (edit>output styles>open style manager) when you have a style selected, there is a drop down menu with the choices “Style Info” (displayed as the default) and “Style Preview” which shows a number of examples: Book, Journal article and Chapter/Section in a book. This can be quite helpful when trying to find out whether a specific style is close to or exactly what you need.