Comment Baen Ebooks. (Score 1) 443
For eBooks (if you like fantasy/SF) I've found Webscription (Baen books) to be a very very good service.
Start there. They have a fairly large library, with quite a few books for free download. No DRM, fairly inexpensive (think $4-$7 per book) and downloadable in just about any format you'd want.
Once you've created an account, those books will stay available on your account page for download on whatever device you want it on.
I've put this same thing in several threads over the last few years, but I think they're still worth mentioning