The ones that you clicked on the title and were utterly fascinated by the subject matter.
For me, anything where Stranger On A Train has dove right in, headfirst. 
Planes and treadmills. Oh the joy!
I like the various rationalizations about why hot water freezes faster than cold, a premise I have yet to believe. I’m sure it’s just badly designed experiments.
how to build a deathstar
The discussions on the Political Compass were very good. Here is the last one; it includes links to the others.
Regards,
Shodan
Long ago, someone asked, “If you could eliminate one species, would you? Which one?” I thought this question was too easy (HIV or the malaria parasite seemed like obvious choices), so I altered it slightly: “If you could change all members of one species into wiener dogs, would you? Which species?” I still think about it sometimes.
All those dealing with cosmology, the Universe, or quantum mechanics. Not that i understand any, but they are fascinating.
And I agree about any with posts by Stranger. There seems to be no limit to his knowledge about anything arcane.