Misfortune is only to be expected in the 13th novel of The Dresden Files, and you can't get much more unlucky than dead. But despite being a ghost, Harry's not done facing trouble, even if he doesn't have a body of his own to cope with it: just his wits, his memories, and a whole lot of Shout Outs.
In the first chapter, Harry references one of the running gags from Terry Pratchett's Discworld:
Harry: "For crying out loud, didn't I just say that death wasn't scary anymore? Tell that to my glands."
Which is fair enough, as Harry'd just asked him "Aren't you a little short for an archangel?" and Uriel likely knew Harry had just argued Wars over Trek in Molly's mental Star Trek-themed command hub. Which brings us to:
Harry "Will Smith"-ing during his fight with the lemurs.
Mort complains about how everyone goes all Lifetime about Mister.
Harry defines all of his neat abilities as a ghost in terms of which Marvel Comics mutant has those powers: Nightcrawler is one prominent example, as is Shadowcat. He's a bit annoyed when he can't think of one that could see in the dark. Although personally, Harry suspects Colossus would've been more fun.
Harry also compares his non-ghostly "wizard senses" to "spider sense".
Mort's hybrid car is said to boast a computer that "Looked like it could have run the NYSE and NORAD, with enough attention left over to play tic-tac-toe. Or possibly Global Thermonuclear War." in a shout-out to WarGames.
When Harry criticizes Mort's car, Morty snarks back that Harry used to drive Herbie's trailer-park cousin.
One of the Alphas is a young woman whose werewolf form is lightly-built and colored a bit like a coyote. In trying to recall her name (Marci), Harry's second guess is "Mercy", which is the name of Patricia Briggs' coyote-shapechanger heroine; like Harry, she hangs out with werewolves and fae.
Harry starts to sneak into the Grey Ghost's lair, then quits with the Scooby-Doo action when he realizes his ghost-self can't make noise anyway.
Sir Stuart's line about wraiths not knowing pity, nor restraint, prompts Harry to suggest fear as another thing they don't know. Almost certainly a Terminator reference.
Aristedes' blade is like a Bowie knife designed by H. R. Giger.
Harry tries some of the same words Gandalf used to try to open the door to Moria on the entrance to the Corpsetaker's lair. And calls her a tasteless bitch for not reading Tolkien when it doesn't work.
Uriel reveals that one of the Fallen tempted Harry to arrange his own death with seven words and that as a result Uriel can use seven words to help Harry. Considering that Jim Butcher and Patrick Rothfuss are friends, this may be a shoutout to The Name of the Wind.
At one point Harry says that for someone to get away with calling Murphy "Karrie", they'd have to be "a Terminator. From Krypton."
Inez gives a shout out to Jim Butcher himself, when she tells Harry "They'll write books about you."
Harry wants to dismiss the latter example because Spider-Man isn't real. Bob retorts that in another universe, he could be real. A case of Fridge Logic when you realize that in our universe, Harry himself is just as fictional as Spidey...
Wait but Luke and Vader are?
Molly's psychic sensitivity is compared to her having great big, honking Dumbo ears that are extremely sensitive to loud noises.
Harry quips "It's like Thunderdome" when the other ghosts gather around him in three dimensions. When they fetch Molly, he greets her with "Two ghosts enter, one ghost leaves."