This is the simple way to display additional attributes of products in layered navigation which helps to filter product easily.
Following are the steps to dislay additional attributes in layered navigation.
1) To add new attribute which you want to display in layered navigation
Go to catalog>attribute>manage attribute
click on add new attribute
now you can create attribute as your required name.But some fields are required as
Catalog Input Type for Store Owner => Dropdown
Use In Layered Navigation => Filterable (with results)
2) click on Manage Label/Options tab
Add options list as your required to display in product list page and as well as in layered navigation.
3) Select any one from in option list of attribute in product edit page.
4) Referesh cache.
5) Now you can see added attributes in your layered navigation.
Enjoy!!!!!!!!!!!
