Baen's been extremely aggressive in adopting ebooks - more so than any other publisher, and currently have two price-points for single books. $15 for the E-Arc, which is the early adopter version, and $6 for most books. You can also buy a bundle for $15. I've spent over $700 at Baen on ebooks over the years.
Macmillan, through their Tor subsidiary, has been working on a deal with Baen. One of the requirements of which (from Baen) was no DRM. I've also seen
reports from a MR member who is a Tor author of the difficulty they were having in trying to get books on Amazon without DRM.