^^ Oops! I'm sorry, I should have said "Organians" -- the race from TOS "Errand of Mercy." They turn up in ENT's 4th season "Observer Effect." I think of them as "Observers" because it will be hundreds of years before they set up Organia for their first contact with Kirk & Co. in TOS.
I thought the Borg episode, "Regeneration," was a nice tie-in connecting "FC" to the Borg of future shows. And I loved the Ferengi episode, "Acquisition," largely because of the actors who played Ferengi, including Jeff Combs, Ethan Phillips from VOY, and Clint Howard.