Phyla and Moondragon reuniting. Shame it all goes to hell not even a few months later.
In the last issue of Vol 2, when Mantis is so glad to see Peter again, she hugs him. D'aww.
Dave Bautista, who plays Drax the Destroyer in the movie, said that he wanted this job more than anything else he's wanted in his life, auditioning 6-7 times for the part and "cried like a baby" when he finally got it.
After filming finished, James Gunn gave Batista a Drax lunchbox to add to his collection of vintage lunchboxes. Meanwhile, Batista gave Chris Pratt and Zoe Saldana some custom WWE Championship belts. Amusingly, the lunchbox features Batista as Drax with a quote from the movie.  Which one? Why, "Finger to the throat means death!" of course.
When interviewed by Bogart the Explorer, Batista theorizes that Drax shares their Filipino heritage, explaining that Drax's skill with knife-fighting makes him "a Kali guru." It sounds kind of adorable to Filipino fans of Marvel and/or Batista.
When Vin Diesel started recording his lines for Groot, he was surprised to be reunited with the sound technician who he had worked with a long time ago when he recorded the titular character of The Iron Giant.
The fact that the movie got made at all is a testament to the faith Marvel has in their properties. It's EXACTLY the kind of thing they set out to do when creating their own production company.
The Stinger goes a step farther, showing that they're even willing to give a second chance to Howard the Duck.
Taking it a step further: let's not forget to mention that when DC attempted their hand at the whole "superhero movie with aliens" thing in 2011, it was a critical and commercial failure. So for anyone to have any interest in this film is a testament to how much of an effect Marvel has on their audiences and how much trust people had in Marvel.
Groot giving a flower to a little girl, who belongs to a group of beggar children. Groot has no money to give her, so he gives her the only thing he can. From the look on her face, it's maybe one of the few nice things she's ever had.
From the Total Film BTS visit, Drax declaring the other Guardians to be his friends. Even the "green whore".
The scene is even more touching (in a weird way) as almost immediately afterwards, Nebula appears and calls Gamora something similar, only to be blasted away by Drax for insulting someone he considers a friend.
Similarly, the featurette introducing Gamora in which she says "I have lived most of my life surrounded by my enemies. I would be grateful to die among my friends."
The soundtrack is simultaneously heartwarming and awesome. Is a collection of seventies hits, both well known and forgotten. Within days, the soundtrack became the highest selling soundtrack of 2014. This soundtrack has groups like Blue Swede, Redbone and 10cc who practically have been forgotten completely. Thanks to the sales of the soundtrack, there is a chance that the hype surrounding it may be able to save them from their current and undeserved obscurity.
The fact that Quill has no quarrel with his co-pilots when he first meets them, despite the fact that Rocket and Gamora nearly killed him.
When Drax warily notes how dark it is aboard Ronan's ship, Groot smiles and begins to release hundreds of glowing seedpods from his body like fireflies, casting the huge room in soft orange light. Everyone is amazed.
From the 5-minute extended clip of the team are being incarcerated at the Kyln, Peter Quill after snarking back and forth with Rocket notices evidence of Rocket's experimentation and gives him a silent sympathetic glance.
Groot grabbing Rocket and diving to safety when The Collector's assistant/daughter sets off the Orb.
It's never stated outright, but given the situation and Groot's gentle-until-provoked personality and protective tendencies towards Rocket, it's probably safe to assume he got involved in that bar fight with Drax on Rocket's behalf.
Quill also performs a similar maneuver on Groot when Rocket crashes his jet into the Dark Aster.
Rocket, Drax, and Groot's ultimately unnecessary attempt to rescue Quill and Gamora from the Ravagers.
When Groot is trying to convince Rocket to go along with the rescue instead of running to the other end of the universe:
Groot: I am Groot! Rocket: I know they're the only friends we ever had!
Quill carrying Rocket out of the jet's wreckage.
Drax stroking Rocket's fur while he mourns over Groot's Heroic Sacrifice. Also counts as a funny moment.
It becomes even more heartwarming when you realize that Rocket looks like he fully expects Drax to say something uncouth, since he was so callous about Drax's own family dying. There's a brief moment of him pulling it together and pulling away before he loses his nerve. The fact that Drax comforts him comes as a genuine surprise to him, because he doesn't think he deserves it.
Yondu deciding to adopt Quill instead of letting his men eat him or handing the boy over to his jackass dad. He's certainly not the best parent by any means, but he does care for Peter in his own way.
Before their last fight, Korath addresses Quill as "Star-Lord", which makes him smirk. It almost comes across as a sign of appreciation.
The fact that Peter has been lugging around the mixtape and walkman, not to mention the cassette player and sound system installed on his ship, means that he has maintained all that equipment for over 20 years! And he's obviously played that cassette many, many times over the past two decades, so to keep all that in pristine condition while gallivanting around the galaxy with no spare parts from Earth just goes to show how much his last connection to Earth means to him.
There's also The Reveal of what's in Peter Quill's unopened gift from his late mother. A second volume of her mixtape, her hand written letter even showing that the Star-Lord moniker came from her. Keep in mind that she asked that he not open it up until she had died, and yet he waits until after everything, including the imagery of his mother once-more asking for his hand, to do so. He's finally made his peace with both her passing and his own failures.
And then what's the first song on his mom's second mixtape? Ain't No Mountain High Enough.
And then Gamora tries her hand at dancing to it, something she couldn't manage before, even to distract Ronan. And Quill's smile shows what he realizes: the love his mother had for him, the love she expressed through her music, is the love the Guardians now have for each other.
When Yondu checks the sphere where it was supposed to contain the MacGuffin, it actually has an old Troll doll in it. Instead of being mad at Star Lord for cheating him of his prize, he just smiles.
Quill could have given Yondu an empty orb — there was plenty of them. Instead, he gave Yondu the one thing guaranteed to have personal meaning to him, given Yondu's fondness for collecting toys. It's no wonder that he smiles at it. Looking at him as he muses, one gets the impression that he strongly suspected this from the start, but would never have opened it in front of Quill to check.
It gets even better; the Troll doll was presumably in Quill's backpack when he was abducted from Earth, meaning it was one of his last souvenirs from his home world. To give it over to his surrogate father figure, as an addition to Yondu's collection of knick-knacks and toys, is subtly nice of him.
Peter saving Gamora by putting his helmet over her head. In Space.
The Guardians — minus Groot, who is pretty much firewood at that point — grabbing hands with Peter as he holds the Infinity Gem in order to split the power and help each other survive.
Including Groot. He comes back from even the tiniest twig. Rocket was holding one of Groot's twigs, splitting the power by 5. Rocket's grief over the "death" of his friend saved a planet.
The best part? None of them knew they'd survive the power of the Infinity Stone. As far as they knew, holding onto Peter could have been their deaths, too, but they still held on anyway.
Dey reuniting with his wife and daughter, revealed to be the pink-skinned aliens among those Rocket protects from the kamikaze necrocraft. Extra points for what's being sung over it: "My love is alive."
Groot saving Drax from drowning.
Gamora laying a hand on Drax's shoulder at the end, followed by Rocket looking back at him and smiling.
Drax realizing he has friends, and individually calling them out as such, even though he hasn't realized "whore" is not a term of friendship; followed immediately by him blasting Nebula because "nobody talks to my friends that way".
Bill Mantlo, Rocket's creator, has been in intensive care since 1992, and got a private screening of the film. He loved it.
Rocket calling the groups goal to stop Ronan a suicide mission is treated seriously by all of the members. Each of them chooses to continue on, fully expecting not to come back at all, for their own reasons. Quill is naturally altruistic, Gamora wants to do some good for once in her life and wants to die among her friends, Drax wants to prevent others from suffering as he has and looks forward to reuniting with his wife and daughter in death, Groot is just naturally nice, and Rocket has a naturally short lifespan.
An odd case between Gamora and Nebula, They are antagonistic rivals who have been transformed in to mass killing machines by a man who killed their families, destroyed their world, tortured and experimented on them and then dubbed them his children. Despite this they legitimately consider each other sisters, even if that doesn't stop them from trying to kill one another, Nebula even states that she hates Gamora the least. In their climatic battle the thought that Nebula was going to preform a Disney Villain Death actually elicits a Big "NO!" from Gamora. Then Nebula decides that while she won't help Gamora, she won't help Ronan either, and exits the battle field.
This extends to their backstories too. When on a mission, Nebula was trapped and Thanos demanded Gamora leave her behind. Gamora defied the Mad Titan and went back to save her, though this would cost Nebula her arm.
Gamora calls Quill "Star-Lord," without any sarcasm or irony by the time the film ends.
A minor one, but when Rocket finds Peter on Xandar, it was nice to see that Peter and Bereet parted ways in an amicable manner. He may be a bit of an inconsiderate dick for forgetting her name AND that she was sleeping on his ship, but it's obvious that Peter treated her good.
Chris Pratt apparently STOLE his Star Lord costume from the set. For the sole purpose of having it availble so he could show up in costume to visit sick children in the hospital that might want to meet Star Lord.