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, '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?