I don't know what you call this button but it is a crossover between a drop down list/mega menu and a button.

Very simple example:
Google's "More" button across the top next to News/Videos/Maps and then there is the "More" button with the other options. 
https://www.google.com/#q=dog

Next example:
Your site! The skin selecting drop down:
http://demos.telerik.com/aspnet-ajax/grid/examples/overview/defaultcs.aspx

The option for a full fluid width like this would be nice along with the possibility of a fixed or fitted width. I also really like the animated arrow up/down.

But the mega menu example is Amazon:
http://www.amazon.com/

Their buttons/drop downs in the top right for "Your Account", "Try Prime", "Cart", and "Wish List".

These are beautiful and would be great functionality. It would also be ideal if the button/link itself that triggers the drop down doesn't have styles like the skins so they can easily be integrated into a website's existing navigational items and site design.