The suits worn by Jules and Vincent are similar to what is worn in quite a few Asian Action films, Tarantino himself has talked about "A Better Tommorow II" as being the main inspiration behind the black and white. Also quite a few surf bands from the late 1960s would perform in black suits and thin black ties...and Pulp does have Surf Music.
The sodomy scene in the Pawn Shop along with the hillbilly esque characters are obviously inspired by Deliverence.
The way Butch searches for a weapon in the pawn shop reminded me of a scene in "Last House on the Left" in which the father character (out for revenge) looks through his garage for a weaon suitable to kill the convicts.
butch, with a sword drawn on Zed saysm "You want that gun Zed? Go on, pick it up. I want you to- There ya go!" is similar to a line in Rio Bravo in which John Wayne and Dude go into a saloon searching for a shooter, they have all the patrons remove their guns, one guy tries reaching for his gun and John says to him, "you want that gun? Pick it up, I wish you would"
A reference to Ragin Bull is how Butch waits inside the Pawn Shop with a beer bottle, then SMASHES it on Marcellus upon entering. In Raging Bull Joe Pesci does this outside a restuarant.
Lance selling the heroin to Vincent reminded me of theguy in Taxi Driver selling Travis the guns.
A street fight busts out in Foxy Brown and a shot is used similar to that of Butch punching Marcellus.