Well, 'The Soft Weapon' is among the top. It has an interesting plot where an alien weapon with unique properties is discovered. 'At the Core' is also a notable one. It delves into the mysteries of a planet's core and what might be found there. And 'The Borderland of Sol' is quite good too, dealing with the idea of the outer regions of our solar system and potential encounters there. There are other great ones too, but these are some that come to mind quickly.
One of the best Larry Niven short stories is 'The Jigsaw Man'. It presents a future society where organ donors are treated in a rather extreme way. 'Bigger Than Worlds' is also a gem. It explores the concept of megastructures and how they might function in a fictional universe. 'All the Myriad Ways' is another great story. It gets into the idea of parallel universes and how different choices can lead to vastly different outcomes. There are more stories in the list, but these are some of the more prominent ones.