Okay SO.
Gaia items that are referenced from things outside Gaia. Let's find them.
I'll start with a few of the more obvious ones (to me, anyway):
Dionaesil =
Audrey 2 from the Little Shop of Horrors. Carnivourous, sentient, venus-flytrap lookalike? Check. And look at the name of that pose- "Feed me, see? More!" = "Feed me Seymour!"
Stainless Steel Bonesaw=
The TF2 Medic's Bonesaw.Think it's a coincidence? Check out the item description. "I AM THE UBERMENSCH!" That's also one of the Medic's ingame lines.
GAU-3 Sasha =
The TF2 Heavy's minigun. Which is also named Sasha. (Or Sascha, if you want to be picky.) There's a reference to the Heavy's "Meet the" Video in the item description, too.
Improvised Flamethrower =
TF2 Pyro's flamethrower. Not as direct as the others in terms of look, but check out the item description. "...Also good for making the invisible, visible!" That's what one of the Pyro's specialties is. Spy-checking.
Hyde's Bloodlust and
Jekyll's Morality = Dr Jekyll and Mr Hyde. Not rocket science.
Oh hell, all of the Playwright items are super obvious, we all know that.
And i'm lazy, so i'm stopping here. Anything you guys have picked up on?