I've remembered another one: TNG
The Emissary (which I'm watching right now on SciFi Channel). It's the only episode that treated Klingon mating seriously and made it look hot instead of 1) intentionally ridiculous or 2) intentionally ridiculous and a source of comedy. Together with TOS
The Enterprise Incident, it's one of the few episodes that feature interesting and actually hot/sensual alien eroticism.
Spock and Zarabeth in TOS
All Our Yesterdays was also quite sexy. In fact, any time that Spock got passionate was very sexy.
This scene with Pon-Farr-stricken Spock and Nurse Chapel in
Amok Time is quite sexy (even though I don't really like Chapel).
ENT
Harbinger wasn't bad, but the T'Pol/Trip scene in T'Pol dream in
Damage (I think it was in that episode) was sexier, though also disturbing.
DS9 A Simple Investigation is probably one of the more sexual Trek episodes out there.
The sight of Odo naked in bed is completely repulsive to me. Obviously though, mileage varies
Well, I don't find the sight of scantily-clad Rene Auberjonois very appealing, but I'd have to agree that the scene and the story was well done, and it was interesting to see Odo have a humanoid sexual experience for the first time. I'm one of those who think that was one of the few good romance-of-the-week episodes.
As an opposite example, I found Jonathan Frakes attractive in the early days of TNG, but every Riker love scene was painfully unsexy and embarrassing. Putting him in clothes like
this (granted, that was intentionally silly) didn't help matters.
Of course there are lots of episodes where people take off their clothes, show skin etc. - sure, I could start listing the episodes where an attractive guy took his shirt off or cast members wore very tight clothes (like
Bread and Circuses - out heroes in tight shirts with short sleeves, all sweaty and fighting in the arena

Spock in that tight shirt

not to mention
Flavius Maximus, the hot rebel gladiator

) but I'm not sure if that's enough to fit what the thread is about.
