People:
* Leonardo da Vinci
* Lady Gaga
* LeBron James
* Lin-Manuel Miranda
* Lizzo
* Luther King Jr.
Places:
* London
* Los Angeles
* Lake Superior
* Las Vegas
* Libya
* Luxembourg
Organizations:
* Lego
* L'Oréal
* Lyft
* Lowe's
* League of Legends
Things:
* Leica (camera brand)
* Lamborghini (car brand)
* Levi's (jeans brand)
* Lincoln (car brand)
* Louis Vuitton (luxury goods brand)
Literature & Media:
* Lord of the Rings
* Little Women
* La La Land
* Lost (TV show)
* Life of Pi
This is just a small sample, there are countless proper nouns starting with "L"!