vim-apathy automatically sets Vim's 'path' option for various file
types, which helps a bunch of Vim commands usefully discover included
files (gf, :find, [i, and more).
vim-dadbod provides a :DB command, which can send queries through to a
wide variety of database management systems. This includes Redis, which
is awesome.
vim-eunuch provides Vim commands wrapping various UNIX functionality.
The most exciting are :SudoWrite and :SudoEdit, allowing a privileged
file to be edited and saved without having to 'sudo vim' up front.