You can find the list of other participants HERE. I'm #149.
U.N.I.T.--This military organization has been around since classic Who. In some of those earlier generations, the Doctor actually worked with UNIT. There were times in the newer series that they were helpful, other times they seemed like pests. Martha worked for UNIT and that's where she got the Osterhagen Key.
(from the TARDIS Wiki) "The Unified Intelligence Taskforce — formerly known as the United Nations Intelligence Taskforce, and more usually called UNIT — was a military organisation which operated under the auspices of the United Nations. Its remit was to investigate and combat paranormal and extraterrestrial threats to the Earth. UNIT was not the only alien defence organisation, but it was the one with which the Doctor had the closest personal involvement."
Universe (cracks in)--This was another favorite reoccurring theme with my kids. So m uch so that during a road trip one of them was looking at the cloud formation and pointed out the "crack." Another child screamed and yelled "Silence will fall! Beware the Silents." Then it got really good when she paused and said as sweet as ever, "What were we talking about?"
My kids are awesome!