Trivia: In "Human Nature", when John Smith (The Doctor's human identity) is talking about his parents, he says their names are Sydney and Verity. Sydney Newman was the creator of Doctor Who and Verity Lambert was the first producer. (00:30:00)
Rise of the Cybermen (1) - S2-E8
Trivia: Only eleven Cybermen costumes were built, but careful filming made it look as if there were more.
Trivia: Possible Spoiler: At the time of this writing, it is generally believed that the "Mister Saxon" referred to throughout Season 3 will turn out to be The Master. One piece of evidence backing this theory is The Master's penchant for anagrammatic aliases: Mister Saxon is an anagram of "Master No Six," and if it's true, John Simm would be the 6th actor to play The Master. [Russell T Davies (who wrote most of the episodes) has said that the anagram is pure coincidence which was picked up by some people, but was completely unintended. Still interesting regardless.]
Trivia: Jack causes the Clock Tower to light up. At the end, the writer wanted someone to say 'Jack, did you remember to turn off Big Ben?' then have a bomb land on the Houses of Parliament and the Clock Tower. (The Houses of Parliament did get bombed. The joke was to make it all Jack's fault).
Trivia: Bernard Cribbins, who plays Wilfred Mott, once appeared in a much earlier Doctor Who-related story - he played Tom Campbell in the feature film Dalek Invasion Earth 2050 AD, with Peter Cushing as the movie's alternate, human Doctor.
Trivia: The 'Chula' stems from an Indian restaurant where the writer ate.
The Girl in the Fireplace - S2-E7
Trivia: The spaceship was designed in the shape of a key.
Trivia: The wallpapers on the walls were real 1950s design. Some of them cost £100 a roll.
Trivia: At the end of the episode, Astrid is set loose to travel through space and time. Astrid is an anagram of TARDIS, which does the same thing.
Trivia: Originally, Mrs Moore was to die earlier, but her life was extended with every draft.
The Sound of Drums (2) - S3-E12
Trivia: During the episode, the Master is seen watching the Teletubbies on his laptop. This is very similar to an episode during the John Pertwee era where the Master, played by Roger Delgado, is seen watching an episode of The Clangers whilst in prison.
Trivia: The Ood were originally going to be another species from the planet Raxacoricofallapatorius, home of the Slitheen.
Trivia: Freema Agyeman, who later played Martha Jones, plays Adeola in this episode. Russell T Davies later said that by the time he came on set and saw her performance, she had already shot her death scene - if she hadn't, he would have rewritten the episode so that she survived to become the next companion. Hence why Martha references her cousin Adeola in "Smith and Jones."
The Angels Take Manhattan - S7-E6
Trivia: Spoiler: Rory's grave reads "Rory Arthur Williams." This is a reference to his actor, Arthur Darvill.
Chosen answer: 1) When Stephen Moffat took over he ignored a lot of what had been developed before (there is not in-universe answer). 2) It would have killed Rose, so the Doctor absorbed the energy. His body regenerated before the energy could do a significant amount of damage that would prevent regeneration.