In Sparrow, you can easily just get the latter — and the email you're reading if you want, of course.
Hide the Accounts, Folders and Labels Sidebar in Sparrow
To see only the list of messages (and the preview pane if open) in Sparrow:
- Press Command-Shift-M.
- You can also Window | Sidebar from the menu.
To bring back the sidebar, employ the same keyboard shortcut or menu item again.
You can use the keyboard shortcuts Command-1 to Command-7 to switch between Inbox, Starred and all other labels and folders.
(Updated July 2011)