The entire Phantom Rogue movie is fanservice from beginning to end. Killua watching Gon sleep & then Gon teasing him about it, Illumi being possessive of Killua & calling him cute, Omokage basically says that Pairo's cuteness gives him a boner, Kurapika clinging to Pairo lovingly, Leorio getting embarassed when Gon & Killua tease him about how much he likes Kurapika, Illumi grabs Killua's face & uses as sexy voice tone & gets close enough to almost kiss him, Killua's hostility towards Retz which increases when he finds out she's a girl, Leorio is frequently touching Killua, Pairo seems to be a bit jealous of Leorio, Nobunaga gets all worked up about Uvogen, Hisoka has said something sexually suggestive to Kurapika, Hisoka then creeps Leorio out telling him that he & Kurapika are his unripe fruit just for him, & Omokage refurring to Pairo, Illumi themsels wirth Kurapika & Gon's eyes as beautiful.
Pedoclown doesn't limit himself to shota boys, though. He's also got the hots for Kuroro and Machi.
And then he definitely stares at their butts and chuckles (in the anime he moans), and Killua makes him walk in front. And then Gon comes up with a brilliant plan for not losing at dodge ball (okay, tactically important, bone-breaking dodge ball) that involves as a necessary side effect Killua being slammed into Hisoka's crotch. More maniacal chuckles.
In the 2011 anime remake, they let you know by Episode 5 that Hisoka has the hots for Gon.
In the "Nightmare of Zaoldyck" musical, Hisoka amps the Pedobear act up by 9,000. He even compares Gon to a little green apple then he licks it.
In Chapter 326 Hisoka thinks about how he wants Gon to be saved.
There's also plenty of Gon/Killua. They spend much of the Whale Island arc sharing their feelings and promising never to be apart, and then there's the theme tune lyrics: "I put my arm around your shoulders and hold hands, because I want to stay either your lover or friend" (with shots of Gon next to Killua and Leorio next to Kurapica).
In the Chimera Ant arc, any and all Gon/Killua subtext is dangerously close to crossing into text, what with all the close ups and inner monologues Togashi keeps giving us. And when entire pages are dedicated to Killua's sad little face when Gon tells him that 'he couldn't possibly understand what he's feeling' during the Neferpitou/Gon deadlock, you know something's up.
"Sad little face"? As of the latest chapter, Killua's had a complete breakdown in the middle of a life-threatening fight.
Not to mention Killua stalking Gon and Palm on their date to make sure Gon wasn't attacked by any rogue ants (sure...), and Palm blaming Killua for 'getting in the way' when she splits up with him.
Especially notable during the time when Gon was depowered and they were near a village with a risk of being attacked by ants, where Killua thinks that if ants were to attack, first priority would be to protect Gon even if it meant letting everyone else die.
Killua and Gon have a lot of this together, especially coming from Killua's side. The only thing that really seems to be keeping it firmly in the realm of "subtext so thick you could cut blocks of it out of the air with a knife and sell it as cheap building material" is the fact that they're both twelve, and neither of them seem to have hit puberty yet.
Palm to Killua: "If there's something I can do for Gon, I'd do it gladly. But don't forget...the one most important to Gon is you..."
And in Chapter 326 Killua thinks about how much he wants to save Gon.
In Chapter 326 Hisoka also says that Gon is Killua's "most beloved" and the "spent most time with". 
In Chapter 329 Killua thinks "Gon...I'm almost there...!!"
In Chapter 331 Killua thinks "Just wait a little bit longer Gon!" showing that he's still going all out to save and find Gon.
The movie took another large step in the Ho Yay when Killua went suicidal because he failed to protect Gon.
It also took a large step way earlier in the movie, when Killua gets all Green-Eyed Monster over the fact that Gon comes back from the Let's Split Up, Gang with a new friend. . . until he finds out said new friend is a Bifauxnen, not a boy. Then suddenly he's totally cool with them.
Don't forget after the intro of the movie when Killua watched Gon sleep and Gon noticed it, calling him out on it. Killua then went tsundere about it.
In the "Hunterpedia" chibi segments, on the whiteboard, there is an Ai Ai Gasa with their names under it; this is the equivalent to the US carving your name and your significant other's name into a tree in Japan.
Also in the "Hunterpedia" chibi segments, while talking about Baise and her Nen attack "Instant Lovers", Killua kisses Gon as a demonstration of the move, making Gon fall in love with him with hearts in his eyes and tries to kiss Killua.
In the Greed Island Tutorial chibi segments, Gon seems to be jealous of Killua's crush on Gold Dust Girl, as Killua made him use a Transform on a card to make one and Gon's voice was clearly one of displeasure.
Madhouse themselves seem to ship the two, as they add additional scenes just to show more Ship Tease between the two, such as the scene where Killua pushes Gon out of the way of Kite's bullets and Killua ends up straddling Gon in a protective fashion.
"The Last Mission" movie oozed Killua and Gon moments out the wazoo, from dramatically serious to their normal interactions to hilarious jabs at the fans who ships them with the scene of them in the "your face here" cutout.
Killua has a habit of staring at Gon and blushing whenever Gon compliments him or is generally sweet to him; which some fans take as Crush Blush.
Killua's Tsundere nature comes out mostly when around Gon, he usually shows his deredere side to Gon, but whenever Gon compliments him or is sweet to him, Killua's tsuntsun comes out.
Gon- The first thing I'm gonna do when I meet Ging is introduce him to Killua, my best friend in the world.
Killua- *blushes* Shut up, that's embarrassing!
Kurapika and Leorio bicker like a married couple ever since they met and even talked to each other. It goes that far back.
In the same episode, Leorio goes off to find Kurapika when he burns the a Kurata ship. He even outright states that he was concerned for Kurapika.
Also in an anime-only episode, Leorio is supposedly lost at sea, and Kurapika is terribly shaken and tries to hold off the operation they were doing just to buy time for Leorio, and eventually Gon, to get back on the ship.
Then there's the more nicer moments where they agree on things, such as the nice phone call talk at the end of the first anime. Even more noticeably, they talk with each other more often than to the other two in the group.
When Leorio relents and tells Kurapika its okay to stick to his ideals in the Hunter Exam arc, Kurapica says his name with an endearing tone.
In the Nightmare of the Zaoldyecks musical, Leorio seems a little too eager to get naked in the hotsprings with Kurapika.
Feitan has his own creepy brand of this, if you take the fact that he wanted to torture Gon slowly, combine it with the fact that he reads books by Trevor Brown (to paraphrase from the wikipedia article, the guy draws surreal doll-fetish kiddie-torture-porn), and, um, yeah...
There's also those two super-minor characters in the Hunters' Exam, who have hilarious amounts of Ho Yay in the anime-only test involving the boat.
Come on, This Troper was the only one to notice Killua's constant blushing toward Kurapika in the OVA? Even the manga shows his uneasiness when the blonde smiled (for the first time in 20 episodes, no less).
Nope; you absolutely are not.
Shaiapouf and the king have this, mostly from Shaiapouf's side. "So I can build a kingdom. The king's and my kingdom."
As of Chapter 299, the Ho Yay between Shiapouf, Yupi, and the king has reached critical mass. All personnel are required to evacuate immediately. This is not a drill.
Nobunaga and Uvogin, so much that the former really wanted to kill Kurapika for killing the latter.
Uvogin and Shalnark are quite close as well, as Uvo kissed Shalnark on the cheek as thanks for giving him information on Kurapika, which shocked Shalnark, and Shalnark held a Longing Look as he watched in concern as Uvogin left to find Kurapika.