Maybe Tarjan's strongly connected components. That's one I've implemented at some point at least.

This is one of my favorites:

https://en.wikipedia.org/wiki/Splay_tree

Aside from inventing a bunch of individual algorithms, Tarjan is also known for introducing various theoretical techniques that are now considered fundamental. Most notably, amortized analysis.

His Turing award writeup gives a pretty broad overview of his research contributions: https://amturing.acm.org/award_winners/tarjan_1092048.cfm