Okay. I've got two for ya...

1) When Buffy says 'Back off, Pink Ranger!' when they are in the middle of fighting, (before they know that they are both slayers) it is an obvious reference to the fact that Buffy's stunt double (Sophia Crawford) also used to do the stunts for Pink Ranger on the Mighty Morphin Power Rangers.

2) This one is slightly more subtle. Buffy tells Kendra to watch the in-flight movie on her way home, except if its a 'movie with a dog in it and Chevy Chase.' This is a referral to 'Funny Farm'-a 1988 movie starring Chase that Gellar had a small, uncredited, role in.