Well, there’s that new Hobbit movie opening next week. Gandalf and the ghost of Obi-Wan join Forces to battle and defeat Smaug, Sauron, and the next Sith Lord.
ETA: With a cartoon before the main feature, in which Roger Rabbit and the Pink Panther mix it up with Jar Jar.
The League of Extraordinary Gentlemen (2003) was a crossover - or messy mischmasch - of characters from popular 19th century novelists including Rider Haggard, Verne, Stoker, Wilde, Twain and Stevenson.
R2 D2 & C-3PO were depicted in Raiders of the Lost Ark
Howard the Duck had a cameo in Thor: The Dark World.
Going forward, I’d like some of the superheroes in various movies at least acknowledge that other famous superheroes exist. I realize a crossover isn’t an option, but having Spiderman say “Where are The Avengers when you need them?” would be awesome.
I like *Snow White and the Three Stooges * (1961) myself. It also includes at least one pretty cool figure skating (!) sequence (the lead is an Olympic gold medalist) and some ventriloquism, if I recall…
Are you sure you don’t mean Guardians of the Galaxy?
By the way, in-jokes like R2D2 and C3P0 being in the wall art in Raiders is nothing new. R2D2 was sculpted into the Mother Ship for Close Encounters of the Tird Kind, and actually made it into the final film. There’s a fighter plane from Apocalypse Now sculpted there, too, but it didn’t make the final cut.
Back in the 1930s and 1940s, Universal Pictures regularly had their popular monsters (Frankenstein, Dracula, the Wolfman) cross paths. Two or more of those monsters appeared in:
Frankenstein Meets the Wolfman
Abbott and Costello Meet Frankenstein
House of Frankenstein
House of Dracula.
Xena: Warrior Princess goes to Gor. You know there’s gonna be fighting. And arguing. And fighting!
Ninjas vs. Pirates of the Caribbean
Conan Meets Xena. At first, they are enemies, then they are friends. Then they are friends with benefits. And in the meantime, they stab a whole lot of bad people. Lawyers, Congressmen, and cannibals, oh my!
Enterprise vs. a Star Destroyer. Actually someone has already done it on Youtube. A lot.