Episode 3 in Season 1 is entitled "The Turk" after the eponymous chess playing computer in the episode. Several electronic chess players have been named such in reference to the original "The Turk", an eighteenth century hoax. The original was a box with a mechanical human upper torso that would move chess pieces, within the box a midget would sit and manipulate the arms with levers.
Absentee Actor: Summer Glau is the only actor to appear in every episode, especially season 2.
Actor Allusion: Shirley Manson, who portrayed the liquid metal Terminator known as Catherine Weaver, played a killer robot in a music video. When we first find out that Shirley Manson is a T1000, she has disguised herself in the form of a urinal. During the height of her fame with Garbage, Shirley Manson wrote her Top Ten Commandments of Love, which included the immortal line "I want a man who will let me pee in his belly button". And when Savannah tells Catherine that John Henry has to be the one to sing her father's song with her, because she (Catherine) can't sing.
Cromartie takes the form of an actor who'd starred in a Conan the Barbarian ripoff. Now, who played Conan again?
Continuity Nod: Multiple references to events in the first two movies, even a few in-jokes referring to the third movie.
Sarah's death from cancer in the timeline averted by their jump forward is a ref to Sarah dying from Leukemia between T2 and T3.
The picture of Sarah that Kyle Reese carries around as a good luck charm in the future is a re-creation (with the new actress) of a very similar pic seen in the first movie. Derek finds it burned when he gets back to the camp, revealing that he missed the Terminator attack from the first film.
In the episode "Alpine Fields," Lauren's father is the same actor who played Dobson in Firefly. Seeing him and Summer in the same scene together without him pointing a gun at her and using her as a human shield is somewhat surreal.
The Persian emissary from 300, the one Leo kicks down the well, is a resistance fighter.
Irony as She Is Cast: Catherine Weaver is played by Shirley Manson of Garbage fame, and she even performed the cover of "Samson and Delilah" that opened Season 2, but Savannah notes that she can't sing.
The Other Darrin: Sarah, John, Dr. Silberman, Mrs. Dyson, played by different actors than their film equivalents
Throw It In: While training with firearms for the pilot episode, Summer Glau was hit in the face by an ejected bullet casing. Rather than cover up the resulting mark with makeup, the injury was left visible on Summer's face throughout filming for the pilot, as one of the "wounds" Cameron picked up in combat.
What Could Have Been: Apparently the Season 1 high school stories would have tied into the Skynet plot...somehow. That's all the crew has let us know after the season was cut short by the writer's strike and they decided to abandon the stories entirely in Season 2.