Or for a real blast from the past , how about the original ST episode where Kirk and the crew go back to the 60's to stop the Nuclear rocket from being launched / tampered with .
That too. :p
How about bringing back Trelane (TOS: The Squire of Gothos)?
Did you play the old Star Trek game "Judgment Rites"? They brought back Trelane for one "episode", and this time he had a strong fascination with World War I aviation. The Enterprise even fought Trelane's Red Baron triplane in space! It had phasers instead of machine gun ammo. :p