Buffy the Vampire Slayer

Buffy the Vampire Slayer was a hit American television show centered around Buffy Summers, a vampire slayer; as the name implies. The show, as well as the character Buffy as been mentioned on Charmed several different times.

The Power of Two
While in a abandoned cemetery attempting to find the headstone of Jackson Ward, in order to vanquish his ghost. Phoebe asks Prue "Where's Buffy when you need her?"

Bite Me
This episode is often known as the episode based around Buffy The Vampire Slayer, as it is mostly about vampires. Leo made a reference to the show changing television networks due to scheduling conflicts and also Brian Krause's hair for that episode, was spiked up in the way a character on Buffy, Angel sports it.

Notes and Trivia

 * Both shows feature an episode based around a particular character stuck in an alternate reality that she is currently in a mental hospital. It was often argued that BTVS did that episode first, Charmed's version of it actually aired first, on November 8th, 2001 with BTVS's one airing three months later on the 12th.