It appears that Castle yielded -- Nikki is not naked on the cover.

Voiceover Promo: There are two kinds of folks who sit around thinking about how to kill people. Psychopaths, and mystery writers. I'm the kind that pays better. I'm Rick Castle.

(watching the models used for the photoshoot for Castle's book walk out)
Ryan: We should have photoshoots here more often.
Esposito: Hey Beckett, how come you don't wear a uniform like that?
Beckett: Because I don't want to get paid in singles?

(Castle and Lanie, in the coroner's van, had a body stolen from them at gunpoint)
Ryan: What, no brain damage?
Lanie: He has some, it happened way before tonight and was probably self-inflicted.
Castle: Ahhhh, good times!

Martha: Ehhh, they've remade Fame, and A Christmas Carol, has Hollywood totally run out of ideas?
Castle: Well, they just optioned Asteroids, the video game, so my guess is yes.

Lanie: Someone... operated on him.
Beckett: Operated?
Lanie: They cut him open and took all of his organs out.
Castle: Somebody hated his guts...

Esposito: You speak Russian?
Beckett: Semester in Kiev between junior and senior year.

Castle: We make a pretty good team, you know. Like Starsky and Hutch. Turner and Hooch.
Beckett: You do remind me a little of Hooch...

Starsky and Hutch was an exceedingly popular but cheesy 70s TV buddy-cop drama which was "remade" as a 2004 movie with Owen Wilson and Ben Stiller in the title roles, along with Vince Vaughn.

Turner and Hooch was a 1989 "buddy cop" comedy, too, starring Tom Hanks in one of his earlier comedic roles. The "buddy" in this case was a French Dogue de Bordeaux, a rare breed of dog originally bred in the 1600s for pit fighting. The breed of dog bears a resemblance to a mixture of a Shar Pei and a British Bulldog -- lots of excess folds of flesh and one heck of a lot of drool and slobber, a component the movie made substantial comic humor out of... The breed is "Ugly but still sort of winsome somehow", like many bulldogs are.

(looking up at a dead body in a tall tree)
Castle: It's raining men.

It's Raining Men is the title of a popular 1982 song by the one hit wonder, The Weather Girls. The song is considered a camp classic, a dance anthem, a classic female anthem, and also has become a gay anthem.