How many can you spot?
I got Carlotta Valdez (from Vertigo)
The dances and Merry Widow waltz at the start of Merrily We Dance (from Shadow of a Doubt).
The writer's beach house from North By Northwest (Roger Deakins mentions this)
The boat and sub scene from Lifeboat.
Didn't Michael Gambon's narration sound like Hitchcock
Security at the studio gate was called Scotty (Vertigo)
Keep them coming.
"Mr. and Mrs. Smith" (1941)
In "Merrily We Dance" Allegra is bored by Monty, but apparently needs his money (?) to feed the monkey with Biff at Lake Onondaga. The expression "(that) suits me" in the "Allegra & Biff" sequence is also used repeatedly in Hitchcock's "Mr. and Mrs. Smith"; the first time, when Mr. Smith (Robert Montgomery(!)) has threatened Mrs. Smith that she would get no more money from him, and she leaves the taxi to enter the store, that turns out to be her new workplace.
"The Birds" (1963)
In "The Birds" the gas station blowing up is owned by the fictitious(?) company "Capitol Oil". Soon Hollywood's old studio system, "Capitol Pictures" is a part of, would "blow up".
Baird Whitlock (thanks to felixreidenbach)
Albert Whitlock: famous matte artist, contributed to nine of Hitchcock’s movies.
http://www.imdb.com/name/nm0926087/
Seslum (director of the sailor musical with Burt Gurney)
"The slum": Hitchcock has been expressing his resentment of theatre actors and writers coming to film with the attitude of "slumming", working in the medium for money, but disdaining it. In "Hail, Caesar!", the Communists (like Seslum's star Burt Gurney) disdain Capitalism, but use it to "make a little dough".