If you live in the US and have a library card, try Overdrive. You can check out a huge catalog of eBooks for essentially free (since it’s paid via your local library).
Overdrive ebooks are DRMed (or at least the majority of them are).
Overdrive primarily uses Adobe's DRM system. You can "liberate" the titles with the use of the DeDRM toolset or get the resources directly off their "libby" platform, which simply requires reassembling the assets into an EPUB
Looks like some people are forgetting the first rule of Fight Club.
I know you can break it, but this is in response to someone asking a question about how to buy DRM-free ebooks.
It’s not too hard to break this DRM. My library lets me ‘borrow’ ebooks and sometimes they are due back and I haven’t finished them.