Harvey Birdman, Attorney at Law Season 4 Episode 2

Hulk:
"You wouldn't like me when I'm Hungry/Horny" is related to the original phrase, "You Wouldn't like me when I'm angry".

Heisenberg's Uncertainty Principle:
The box of Heisenberg Brothers bagels features the equation of Heisenberg's Uncertainty Principle, an important result of quantum physics. This is also why Harvey answers Potomus' question with "I'm uncertain".

The Lord of the Rings:
The scene where Reducto was acting, his voice was highly squery, and sitting in a creepy pose resembles the character Gollum from the Lord of the Rings trilogy.

The Incredible Hulk (1978-1982):
This episode uses several elements of the TV show starring Bill Bixby and Lou Ferrigno. Potamus being exposed to radiation, his irises changing color when he was angered, indirectly warning people that he could harm them, etc. Of special note is Potamus seeking Judy's help in controlling his rage (a running them of the show, as David Banner always moved on at the end of an episode), and finally, the end credits where Potamus is walking on the road somewhere and the soulful music playing over the credits. In the The Incredible Hulk television series, every episode ended in this fashion. Unfortunately, it wasn't the same piano piece, which was called "The Lonely Man"

The Incredible Hulk:
Peter Potamus turning into "the creature", several copied scenes from the 2003 feature film Hulk and the ending sequence all point to the cartoon character of the same name.