With Ctrl-Shift-R (jump to file) and Ctrl-T (pop-up type hierarchy) I can happily spend most of my time with only the Editor view showing. You might have to modify them a bit for Mac.
As Amir pointed out CMD + Shift + R should work. If you are looking to not just see the code, but see where the code is in the project, you'll want to make sure your Project Explorer has Link with Editor enabled. Which is at the top right of the Project Explorer tab.