Vanilla Vim allows you to easily fold up blocks of code to save screen space with :fold.

To use it, simply select multiple lines by entering visual select mode with Shift-v and then using :fold. For example:

def foo
  # some
  # very
  # long
  # method
end

…will fold down to:

+--  6 lines: def foo------------------------------------

And you can then reopen it with zo or close it again with zc.