Leon's armored police uniform doesn't look anything at all like that of any other member of the RPD, but it does resemble the SWAT outfit Peter's wearing in the original Dawn of the Dead (1978), 'cept with integrated body armor.
The G-creature chestburster scenes come from Alien, Claire's surrogate mother role towards Sherry mirrors Aliens' Ripley and Newt's relationship, the Tyrants are zombie Terminators, and Ada is derived from Nikita.
In the Underground Research Facility, Mr. X is taken out in a very similar fashion to the T-1000, but unfortunately, with different results.
Try yelling "Smile, you son of a bitch!" as you dispatch the giant croc in the recommended fashion. Just feels right somehow, don't it?
One shoutout from Resident Evil 1.5 that didn't make it into the finished product was a hallway in the jailhouse◊ clearly inspired by a scene from The Serpent and the Rainbow, lined with holding cells containing disturbingly long-armed zombies reaching out through the bars.
It also calls to mind the entrance hall of the pyramid in The Beastmaster, where the Death Guards reach through the slots in the walls.
Birkin's forms seem very reminiscent of the mutating creature in The Thing (1982).
In the hallway outside the room where you get the bronze gear, one of the boards covering up a window has REDRUM written on it.