Anywhere reputable to purchase digital graphic novels (preferably DRM free)?

I've read that Image does but I've yet to try them out. So far I've mostly collected my digital comics/graphic novels from Humble Bundle collections but I'd like something less random. I've been using the Comic Flow app and generally enjoy reading off of my iPad, but the whole DRM thing with Comixology and the Marvel app bugs me. I like owning the digital files for back-up as silly as that may sound.