How to Remove list or grid mode as display option in Magento

You can choose the view option as grid only or list only. The default is Grid/List. You can change it to List/Grid as well.

For this, you have to go to
System->Configuration->Catalog->Frontend

You can change the List Mode.

You can also change the number of products per page on grid or list from there.

From Mukesh Chapagain's Blog, post Magento: Remove list or grid mode as display option