in the movies it's natural webbing from his arm.... and in the tradition of comic movies screwing up comic book history... they've changed the books to match... in "Spider-Man: Disassembled" he goes through a weird change and ends up with natural webbing that just happens to shoot from his arms exactly the same as his web shooters did "WOW!".... so, as of that story, Spider-Man no longer needs web shooters..... although you'd think he'd keep them just in case something went wrong or he used up his supply...... or if he needed to break open a web cartridge over someone to stop them
EDIT: oh yeah... he can also talk to insects and spiders since that story line ..... how did he ever survive without that ability?