I was talking to a colleague recently about what books we were reading, and she reminded me that Stephen King put together a list of recommended reading in his book about craft, On Writing.
As working writers, I think it's possible to keep learning about your craft, even without getting your MFA (and Stephen King agrees). Reading is the best professional development out there.
So anyway, I found this link to Stephen King's recommended reading list/books that influenced his writing. It's already in Goodreads, so if that's how you keep track of books you want to read, you can simply add the ones you're interested in!
Here's the Goodreads list:
Stephen King's Booklist from "On Writing"
And here's the list in a different format from Aerogramme Writers' Studio.