If by Abe, you mean Abe Books, they're a subsidiary of Amazon.

I believe Baen sells some DRM free sci fi books, but it's a smaller catalog.

Pretty sure all of Baen's books are DRM free, and they offer virtually every ebook format around. They even used to include CDs with their hardbacks that would would include a huge subset of their collection. But they aren't a retailer, they're a publisher, so you're only getting the titles they publish.