Prompted by remarks elsewhere I couldn't resist sitting down to watch the episode trailers included in the dvd bix sets. I must say that some of these are damned good trailers getting me juiced to see an episode I already know almost backwards and forwards. It's also interesting to note the trailer's usage of music tracks not actually used in the episode as well as scenes being shown out of order.

Here are what I've noticed different between the trailers and the aired episodes. Please chime in with anything I may have missed.

Shoreleave - Don Juan grabs Yeoman Barrows arm while she still dressed as a princess. Evidently this scene was planned and filmed yet never used in the episode.
The Galileo Seven - We get a brief scene between Kirk and Ferris with dialogue that never appears in the episode. This is actually rather neat because it doesn't really contradict anything because we can assume Ferris had been badgering Kirk more often than what we actually saw ib the episode.
- Flames seen in the shuttlecraft windows as it's burning up. Good thing they didn't use this because it looks really unconvincing as is.
The Menagerie, Part I - When speaking alone with the injured Pike for the first time Spock utters a line about treachery to Kirk that was never used in the episode.
Balance Of Terror - We see the more traditional phaser beams as well as a different accompanying sound effect.
Courtmartial - We see Finney hit Kirk in a way we didn't see in the episode.
Arena - We see a clip of the Enterprise from "The Cage" that never actually appeared in "Arena."
Return Of The Archons - Landru appears as a real person instead of as a mere projection. This is actually kind of cool becasue it would have made the final meeting with the "real" Landru (the computer) more interesting. You could have really seen how the inhabitants would have accepted him as real and still alive.
This Side Of Paradise - The spores erupting have a different sound effect.
- We get to see an unused overhead scene of Spock and Leila not used in the episode.
The Devil In The Dark - We catch a glimpse of the Horta moving through a tunnel that wasn't used in the episode.
The City On The Edge Of Forever - The Guardian has a different sound effect.
- There is an additional shot of Kirk's reaction of horror as Edith crosses the street towards him--he glances towards the direction of the oncoming truck.
Journey To Babel - a neat unused shot of Andorians Shras and Thelev together.
- different phaser sound when Thelev is stunned in the brig.
- different shot of attacking alien ship.
The Trouble With Tribbles - a shot of a tribble in Kirk's command chair.
The Enterprise Incident - an extra unused shot of Kirk nervously twitching in the Romulan brig just before he attacks Spock.
Wink Of An Eye - when Compton first disappears he just winks out without an accompanying visual effect.
Elaan Of Troyius - a shot of McCoy and Spock glancing at each upon discovering Kirk and Elaan embracing. I don't recall this quick shot.
- an unused full shot of the Klingon commander not seen through the bridge viewing screen.
- the colour of the Klingon ship's disruptor fire is a redish hue as opposed to the green hue used in the final version of the episode.
The Way To Eden - the Tholian ship appears in place of the modified Aurora ship.
Requiem For Methuselah - an unused shot of Kirk looking at his now miniaturized ship and not seen in the ship's view screen. This shot actually makes more sense and should have been used, but in fairness ir's not as dramatic although it makes more sense.