[abecedarius]

O'Reilly's ebooks are DRM-free. Kindle version is not.

[cas]

You can easily remove the Kindle DRM using Calibre and some plugins.

[abecedarius]

I choose not to reward publishers of DRMed works with my money. If some of the open-format stuff is too pricey, well, there's plenty to read off in the free world anyway.