DOOS ANYONE KNOW WHERE l CAN DOWNLOAD ORIGINAL SPIDER-MAN COMICS?

I have only been able to find all the comics from 1963 to 1974, but i want to know if i can download any other comics of the series somewhere else. If you know any other sites where i can download comics boooks series by marvel or DC tell me. I'm not only looking for spider-man in particular but also the X-Men, Batman, Teenage Mutant Ninja Turtles, Fantastic 4, Iron Man, Silver Surfer, and other good super heroes.