TOS S01E19, S01E20, S01E21, S01E22

All of the Trek I watched today:

Star Trek: The Original Series, S01E19: "Arena"
Star Trek: The Original Series, S01E20: "Tomorrow Is Yesterday"
Star Trek: The Original Series, S01E21: "Court Martial"
Star Trek: The Original Series, S01E22: "The Return Of The Archons"

Things:

• "Arena" features the first appearance of three classic Star Trek weapons systems:  "Type 1" hand phasers, photon torpedoes, and the first mention of disruptors (although in this case, the "disruptors" being fired at Captain Kirk and his landing party are more like modern mortars than direct energy weapons).  We also see a "grenade launcher" used by Kirk on the surface of Cestus III, which--like the disruptors--is more like a mortar.
• We also see the Gorn for the first time in "Arena".  Although the species will make only two more on-screen appearances in Trek (TAS and ENT), it becomes a fan favorite and features in multiple Star Trek computer games.
• Incidentally, those hissing/growling/grunting noises the Gorn makes during the entire fight?  Tooooootally what I sound like when I wake up in the morning.
• Ah, "Tomorrow Is Yesterday".  Star Trek's first foray into time travel, the old sci-fi trope that will eventually become the bane of many a Trekkie.
• "Tomorrow Is Yesterday" is the first time we get an explicit mention of the rough size of Starfleet (12 Constitution-class starships in service, as of the that time) and the USS Enterprise's operating authority (United Earth Space Probe Agency).  Both factoids will become fodder for debate amongst Trekkies.
  
  - http://ex-astris-scientia.org/articles/ship_classes.htm (section "Constituion Inflation")
  - http://ex-astris-scientia.org/inconsistencies/history-other.htm#uespa
  
  (Correction:  the UESPA is mentioned as an acronym in "Charlie X", but this is the first episode in which it's spelled out.)
• The pouty female computer voice they made Majel Barret-Roddenberry do for "Tomorrow Is Yesterday" is pretty insulting, even if it was intended as a gag (and was probably fairly amusing in the late 1960s).
• Best part of "Tomorrow Is Yesterday"...
  
  Kirk:  "Now you're sounding like Spock."
  McCoy:  "If you're gonna get nasty, I'm gonna leave."
• As silly as the plot of "Tomorrow Is Yesterday" is, I really enjoyed this episode.  It's fun to see a depiction of the US Air Force during the Cold War that was actually filmed at that time, and the CGI graphics in the remastered version (especially the shots of USS Enterprise hurtling toward Sol to achieve the slingshot effect and subsequent time warp.
• Avocado Kirk Shirt (AKS)! (in "Court Martial")
• Although the commodore / admiral guy is wearing a different insignia, it looks like many of the other Starfleet officers in "Court Martial" are wearing the distinctive "arrowhead" insignia of USS Enterprise, that eventually becomes the emblem of Starfleet as a whole.  This may have been intentional, but personally I think it's probably just more likely that they already had tunics with the arrowhead insignia on them that could be used for the other Starfleet officers.
• "Court Martial" fixes both McCoy's and Spock's ranks as Lt. Commander as of TOS Season 1.
• They must've been running low on production funds when they wrote "The Return Of The Archons"--another episode in which much of the action takes place on an Earth-like planet.
• "The Return Of The Archons" features the first on-screen reference to the Prime Directive, although Spock simply states that it means "non-interference" (and he refers to it as "our prime directive", so it possibly wasn't envisioned as The Prime Directive as we know it at the time of the writing of this episode).  The term "prime directive" is also used in another context in this episode, when Kirk and Spock are speaking with the computer Landru...so I'd tend to think that this concept of a capital-P "Prime Directive" has its source in this episode, but isn't fully formed.