I've noticed a few movie references
On the Random Character Brian 2nd encounter, he talking about the drugs he just bought and calls it a boulder, then he says to Niko "You know that movie where that guy's on a mountain getting chased by that giant boulder?" Niko says "No."
I believe this is referencing the classic Indiana Jones scene of running from the boulder.
Also, when visiting the Rotterdam Tower (Empire State Building) with Brucie, he says "If I was that big chimp, I'd climb it too! My arms probably aren't as big but who cares."
It's gotta be a King Kong reference