Hogarth also mentions The Spirit as one of his comic books. Brad Bird is a huge Spirit fan (he also referenced the Spirit in The Incredibles).
The scene where the Giant is chasing Rogard & Mansley's jeep is reminiscent of the T-Rex chase scene in Jurassic Park, complete with Mansley demanding the driver go faster.
"Hogarth? That's an embarrassing name. She might as well have called him Zeppo or something."
The Western that General Rogard was watching when Mansley was contacting him was the exact same one the Dalmatian puppies were watching in Disney's 101 Dalmatians.
The "scary movie" that Hogarth was watching was a shout out to the cheesy sci-fi movies of the fifties (more specifically, The Brain from Planet Arous).
"No. Augh. Aaaaaaah."
Likewise, one of the weapons on the Iron Giant when he goes berserk in vengeance for the apparent death of Hogarth heavily resembles the cannons used by the Martian war machines in The War of the Worlds (1953).
Hogarth's last name is Hughes, no doubt a nod to Ted Hughes, the author of the original book.
The Signature Edition has a moment where the Giant's hand appears to watch Disneyland.