The voice-over in the beginning says Wolfram & Hart has influence in every major corporation, including Weyland-Yutani. This fictitious firm is the ominous company in the Alien films, including Alien vs. Predator (2004).
Another corporation under the Wolfram and Hart umbrella is Yoyodyne. This company is run by the evil Red Lectroids in The Adventures of Buckaroo Banzai Across the 8th Dimension (1984) as a cover for their activities on Earth.
One of the corporations listed as partner of Wolfram & Hart is News Corp, the parent company of 20th Century Fox Television, the studio that produced the series.
This is the second episode named after Harmony, the first being Disharmony (2001). She is the only character to have a second episode named after her. This trend continues with the comic stories Harmonic Divergence, Harmony Bites, Harmony Comes to the Nation, In Perfect Harmony, and Day Off (or Harmony in My Head).
Spike gives up on letting Buffy know he's alive, but she'll eventually discover it on her own in the comic Give and Take.