I’m fond of seeing somewhere the full path to the file I’m currently editing(as opposed to just the file name displayed in modeline). Emacs’s frame title seems like a good place to display such information, since by default it doesn’t show anything interesting. Here’s how we can achieve this:

(setq frame-title-format
      '((:eval (if (buffer-file-name)
                   (abbreviate-file-name (buffer-file-name))

The path will be displayed in an abbreviated manner(/home/bozhidar/ will be shortened to just ~/). If you’d like to see the expanded path just remove the abbreviate-file-name function invocation. If a buffer is not visiting a file, the buffer’s name would be displayed instead.

Prelude sets frame-title-format like this by default.