The statue of the pink panther near Cat Grant's office is the same as the panther statues seen at the top of the clock tower in Back to the Future (1985).
Kara's adoptive mother Eliza Danvers is played by Helen Slater, who previously played the title role in Supergirl (1984).
Kara's adoptive father Jeremiah Danvers is played by Dean Cain, who previously played Superman on Lois & Clark: The New Adventures of Superman (1993).
Dean Cain's character says he knows everything about Superman. This is probably an in-joke as Cain played Superman in the TV show "Lois & Clark".
The green building Supergirl crashes into during the final fight with Livewire is also Miss Patty's Dance Studio in the popular show Gilmore Girls. The building next to it is also seen in the show as well.