OSX Yosemite full screen menu bar
Solution 1:
Like @james_fuller said auto-hiding the doc and maximizing the app window (use the alt key when clicking maximize) will have the requested result. Some apps (Google Chrome) have custom behavior for the maximize button so Shiftit.app can be used to maximize those apps with a simple key command.
Solution 2:
I use Moom and works pretty good:
http://manytricks.com/moom/
It allows you to maximize to fullscreen but keeping the menubar still visible. Different than clicking the green button on the window which enters fullscreen.