Great thread idea. One of the most useful threads I look through a lot is the index thread here:
www.elitefourum.com/t/the-index-of-elite-fourum-articles-updated-march-21-2021/13979/1
It leads to so many greats threads pertaining to all aspects of the hobby and more.
One thread that comes to mind that I love to look through is the Pokémon hidden in the card art thread here:
www.elitefourum.com/t/the-great-pokemon-hidden-in-card-art-thread/24364/1
There are so many interesting connections between cards that are great to see.