I'll be honest these aren't exactly the most 'heartwarming' films ever but I love this line from Pitch Black.
Jack: (After Riddick and Fry come back to get the others.) Never had a doubt!
The fact that Riddick wouldn't let Johns sacrifice Jack to the aliens is actually kinda sweet, even if it led to a horribly bloody death for the aforementioned merc.
Riddick's decision to help Fry get Imam and Jack is as close as one can get to heartwarming in this film. Not to mention the fact that they all held hands before running through the last bunch of aliens, made all the more special by the fact that Riddick initiated the hand holding between himself and Fry. Aw.
There's a quick moment when the crew is holed up inside the containment room and Johns and Fry are arguing. When Fry points out that Johns is being a Dirty Coward, he jumps up to come at her and Riddick intervenes via his shiv pointed at Johns' crotch. It's nice to see that he actually backs her up as leader of the group.
Riddick going back to save Jack from one of the aliens that has her pinned down. We see him struggle with the decision, but the fact that he saves her is as awesome and heartwarming as this film ever gets.