Creating Toolbar Items That Look Like Buttons

I can't seem to figure out how to make my toolbar items look like buttons. Some examples开发者_StackOverflow中文版 of what I'm looking for are the toolbar items in Mail, Safari and Transmission. Are these buttons just simple images, or is there a setting somewhere I'm missing?

They are NSButtons or NSSegmentedControls. Just drag one right into the toolbar from the IB palette.