People:
* Leonardo da Vinci
* Lady Gaga
* LeBron James
* Liam Neeson
* Louis Armstrong
* Lucy Liu
* Lionel Messi
Places:
* London
* Los Angeles
* Las Vegas
* Lake Superior
* Louvre Museum
* Lincoln Memorial
* La Sagrada Familia
Organizations:
* LEGO
* L'Oréal
* Lockheed Martin
* Louis Vuitton
* League of Legends
* Little League Baseball
Things:
* Lamborghini
* La Niña
* La Brea Tar Pits
* Leaning Tower of Pisa
* Linux
Events:
* Lunar New Year
* London Olympics
* La Tomatina
* Lollapalooza
This is just a small sample. There are many more proper nouns starting with "L" out there!