Well, the rumors and speculation have turned out to be true; Wizards of the Coast has teamed up with Onebookshelf to make pdf’s of a bunch of their older products available.
There seems to be a smattering of items from all versions but 0E, and everything’s in pdf format right now, but I’m assuming there will be new things added to the site all the time. There are both books and modules included, and B1 In Search of the Unknown is currently available as a free download to get the ball rolling.
No idea if people who had previously bought access to the pdf’s will somehow be granted access, but UPDATE: Apparently if you previously purchased pdf’s through OneBookShelf, your previous purchases are honored with the re-release. That’s a terrific bit of news. It’s a huge step forward for WotC, and they’ve certainly kept one promise made early on in the 5E development process. I’ll be interested to see what new things get added.