SO. Being a woman who's been "graced" (i use that loosely) with being generously endowed, one of my biggest peeves in the art world is that of improperly drawn boobies. Now i'm not knocking anyone's knockers in particular, but if you're trying to draw NATURAL boobies folks, pornos and nudie mags are NOT your best reference sources.
Again, that all goes out the door if that's the look you're trying for. But, this is for the folks who want the real thing.
For other references, here's a good place to start: [link]