Cemetery Dance has also started testing the digital waters. Right now it looks like the only e-books available on their site are linked to Amazon for download, but I know they sent out an e-mail a couple months ago with an offer for an in-house supported e-book as a test bed. I'm not sure if I ever heard the results of that beta. CD is really involved in the signed and/or limited editions, so it's unclear how e-books would factor into their existing model. As a longtime CD customer, I'd be happy to spend my digital money there instead of somewhere else, and I'm hoping they add e-books as a routine matter to help draw in folks (like me) who are more interested in reading books than keeping them on the shelf.
I'm a HorrorMall fan/customer, too. They have some great niche books that aren't at the library or easily available anywhere else.