Originally Posted by crpgnut 
Could you guys name some great timed quests that you've played and what made the time-limitation special?
The TDE game "Blade Of Destiny" has such a thing : You'll have to chase away the Orcs, or they'll come and run over Thorwal … Game over, then …
The quest of chasing them away is the great, big main theme of the game. However, the time frame is so good, so wide that the party is able to do everything - including research - without having to hurry too much.