Any time Ashley and Leon reunite in Resident Evil 4, especially when they hug after Ashley gets out of the prison area after dealing with two Zealots and the living suits of armor that try to kill her. Then you know it was worth going through hell without a weapon.
Also late in the game when Leon and Ashley use the removal machine to get rid of their plagas, Ashley hugs Leon again in relief.
When boarding Ada's jet ski to escape the island, Leon tells Ashley to "Hang on, sweetheart!", showing that after all they've been through together, he cares about her like he would a daughter or little sister.
Every time Ada Pets the Dog with regard to Leon. It's one thing for Leon to help her, since he's generally that kind of nice guy and would probably do the same for anyone, but it's particularly meaningful for someone like Ada to unhesitatingly put her life and agenda on the line to protect a man she hasn't seen in six years.
The amount of effort she goes to to help Leon too. From Leon's perspective she's aloof and just seems to be passing by. But after playing Ada's story you see her wading through waves and waves of enemies to make sure he's okay, even when she believes he has enough skill and luck to survive no matter what.